diff --git a/go/vendor/github.com/PuerkitoBio/purell/purell.go b/go/vendor/github.com/PuerkitoBio/purell/purell.go
new file mode 100644
index 0000000..645e1b7
--- /dev/null
+++ b/go/vendor/github.com/PuerkitoBio/purell/purell.go
@@ -0,0 +1,379 @@
+/*
+Package purell offers URL normalization as described on the wikipedia page:
+http://en.wikipedia.org/wiki/URL_normalization
+*/
+package purell
+
+import (
+	"bytes"
+	"fmt"
+	"net/url"
+	"regexp"
+	"sort"
+	"strconv"
+	"strings"
+
+	"github.com/PuerkitoBio/urlesc"
+	"golang.org/x/net/idna"
+	"golang.org/x/text/unicode/norm"
+	"golang.org/x/text/width"
+)
+
+// A set of normalization flags determines how a URL will
+// be normalized.
+type NormalizationFlags uint
+
+const (
+	// Safe normalizations
+	FlagLowercaseScheme           NormalizationFlags = 1 << iota // HTTP://host -> http://host, applied by default in Go1.1
+	FlagLowercaseHost                                            // http://HOST -> http://host
+	FlagUppercaseEscapes                                         // http://host/t%ef -> http://host/t%EF
+	FlagDecodeUnnecessaryEscapes                                 // http://host/t%41 -> http://host/tA
+	FlagEncodeNecessaryEscapes                                   // http://host/!"#$ -> http://host/%21%22#$
+	FlagRemoveDefaultPort                                        // http://host:80 -> http://host
+	FlagRemoveEmptyQuerySeparator                                // http://host/path? -> http://host/path
+
+	// Usually safe normalizations
+	FlagRemoveTrailingSlash // http://host/path/ -> http://host/path
+	FlagAddTrailingSlash    // http://host/path -> http://host/path/ (should choose only one of these add/remove trailing slash flags)
+	FlagRemoveDotSegments   // http://host/path/./a/b/../c -> http://host/path/a/c
+
+	// Unsafe normalizations
+	FlagRemoveDirectoryIndex   // http://host/path/index.html -> http://host/path/
+	FlagRemoveFragment         // http://host/path#fragment -> http://host/path
+	FlagForceHTTP              // https://host -> http://host
+	FlagRemoveDuplicateSlashes // http://host/path//a///b -> http://host/path/a/b
+	FlagRemoveWWW              // http://www.host/ -> http://host/
+	FlagAddWWW                 // http://host/ -> http://www.host/ (should choose only one of these add/remove WWW flags)
+	FlagSortQuery              // http://host/path?c=3&b=2&a=1&b=1 -> http://host/path?a=1&b=1&b=2&c=3
+
+	// Normalizations not in the wikipedia article, required to cover tests cases
+	// submitted by jehiah
+	FlagDecodeDWORDHost           // http://1113982867 -> http://66.102.7.147
+	FlagDecodeOctalHost           // http://0102.0146.07.0223 -> http://66.102.7.147
+	FlagDecodeHexHost             // http://0x42660793 -> http://66.102.7.147
+	FlagRemoveUnnecessaryHostDots // http://.host../path -> http://host/path
+	FlagRemoveEmptyPortSeparator  // http://host:/path -> http://host/path
+
+	// Convenience set of safe normalizations
+	FlagsSafe NormalizationFlags = FlagLowercaseHost | FlagLowercaseScheme | FlagUppercaseEscapes | FlagDecodeUnnecessaryEscapes | FlagEncodeNecessaryEscapes | FlagRemoveDefaultPort | FlagRemoveEmptyQuerySeparator
+
+	// For convenience sets, "greedy" uses the "remove trailing slash" and "remove www. prefix" flags,
+	// while "non-greedy" uses the "add (or keep) the trailing slash" and "add www. prefix".
+
+	// Convenience set of usually safe normalizations (includes FlagsSafe)
+	FlagsUsuallySafeGreedy    NormalizationFlags = FlagsSafe | FlagRemoveTrailingSlash | FlagRemoveDotSegments
+	FlagsUsuallySafeNonGreedy NormalizationFlags = FlagsSafe | FlagAddTrailingSlash | FlagRemoveDotSegments
+
+	// Convenience set of unsafe normalizations (includes FlagsUsuallySafe)
+	FlagsUnsafeGreedy    NormalizationFlags = FlagsUsuallySafeGreedy | FlagRemoveDirectoryIndex | FlagRemoveFragment | FlagForceHTTP | FlagRemoveDuplicateSlashes | FlagRemoveWWW | FlagSortQuery
+	FlagsUnsafeNonGreedy NormalizationFlags = FlagsUsuallySafeNonGreedy | FlagRemoveDirectoryIndex | FlagRemoveFragment | FlagForceHTTP | FlagRemoveDuplicateSlashes | FlagAddWWW | FlagSortQuery
+
+	// Convenience set of all available flags
+	FlagsAllGreedy    = FlagsUnsafeGreedy | FlagDecodeDWORDHost | FlagDecodeOctalHost | FlagDecodeHexHost | FlagRemoveUnnecessaryHostDots | FlagRemoveEmptyPortSeparator
+	FlagsAllNonGreedy = FlagsUnsafeNonGreedy | FlagDecodeDWORDHost | FlagDecodeOctalHost | FlagDecodeHexHost | FlagRemoveUnnecessaryHostDots | FlagRemoveEmptyPortSeparator
+)
+
+const (
+	defaultHttpPort  = ":80"
+	defaultHttpsPort = ":443"
+)
+
+// Regular expressions used by the normalizations
+var rxPort = regexp.MustCompile(`(:\d+)/?$`)
+var rxDirIndex = regexp.MustCompile(`(^|/)((?:default|index)\.\w{1,4})$`)
+var rxDupSlashes = regexp.MustCompile(`/{2,}`)
+var rxDWORDHost = regexp.MustCompile(`^(\d+)((?:\.+)?(?:\:\d*)?)$`)
+var rxOctalHost = regexp.MustCompile(`^(0\d*)\.(0\d*)\.(0\d*)\.(0\d*)((?:\.+)?(?:\:\d*)?)$`)
+var rxHexHost = regexp.MustCompile(`^0x([0-9A-Fa-f]+)((?:\.+)?(?:\:\d*)?)$`)
+var rxHostDots = regexp.MustCompile(`^(.+?)(:\d+)?$`)
+var rxEmptyPort = regexp.MustCompile(`:+$`)
+
+// Map of flags to implementation function.
+// FlagDecodeUnnecessaryEscapes has no action, since it is done automatically
+// by parsing the string as an URL. Same for FlagUppercaseEscapes and FlagRemoveEmptyQuerySeparator.
+
+// Since maps have undefined traversing order, make a slice of ordered keys
+var flagsOrder = []NormalizationFlags{
+	FlagLowercaseScheme,
+	FlagLowercaseHost,
+	FlagRemoveDefaultPort,
+	FlagRemoveDirectoryIndex,
+	FlagRemoveDotSegments,
+	FlagRemoveFragment,
+	FlagForceHTTP, // Must be after remove default port (because https=443/http=80)
+	FlagRemoveDuplicateSlashes,
+	FlagRemoveWWW,
+	FlagAddWWW,
+	FlagSortQuery,
+	FlagDecodeDWORDHost,
+	FlagDecodeOctalHost,
+	FlagDecodeHexHost,
+	FlagRemoveUnnecessaryHostDots,
+	FlagRemoveEmptyPortSeparator,
+	FlagRemoveTrailingSlash, // These two (add/remove trailing slash) must be last
+	FlagAddTrailingSlash,
+}
+
+// ... and then the map, where order is unimportant
+var flags = map[NormalizationFlags]func(*url.URL){
+	FlagLowercaseScheme:           lowercaseScheme,
+	FlagLowercaseHost:             lowercaseHost,
+	FlagRemoveDefaultPort:         removeDefaultPort,
+	FlagRemoveDirectoryIndex:      removeDirectoryIndex,
+	FlagRemoveDotSegments:         removeDotSegments,
+	FlagRemoveFragment:            removeFragment,
+	FlagForceHTTP:                 forceHTTP,
+	FlagRemoveDuplicateSlashes:    removeDuplicateSlashes,
+	FlagRemoveWWW:                 removeWWW,
+	FlagAddWWW:                    addWWW,
+	FlagSortQuery:                 sortQuery,
+	FlagDecodeDWORDHost:           decodeDWORDHost,
+	FlagDecodeOctalHost:           decodeOctalHost,
+	FlagDecodeHexHost:             decodeHexHost,
+	FlagRemoveUnnecessaryHostDots: removeUnncessaryHostDots,
+	FlagRemoveEmptyPortSeparator:  removeEmptyPortSeparator,
+	FlagRemoveTrailingSlash:       removeTrailingSlash,
+	FlagAddTrailingSlash:          addTrailingSlash,
+}
+
+// MustNormalizeURLString returns the normalized string, and panics if an error occurs.
+// It takes an URL string as input, as well as the normalization flags.
+func MustNormalizeURLString(u string, f NormalizationFlags) string {
+	result, e := NormalizeURLString(u, f)
+	if e != nil {
+		panic(e)
+	}
+	return result
+}
+
+// NormalizeURLString returns the normalized string, or an error if it can't be parsed into an URL object.
+// It takes an URL string as input, as well as the normalization flags.
+func NormalizeURLString(u string, f NormalizationFlags) (string, error) {
+	parsed, err := url.Parse(u)
+	if err != nil {
+		return "", err
+	}
+
+	if f&FlagLowercaseHost == FlagLowercaseHost {
+		parsed.Host = strings.ToLower(parsed.Host)
+	}
+
+	// The idna package doesn't fully conform to RFC 5895
+	// (https://tools.ietf.org/html/rfc5895), so we do it here.
+	// Taken from Go 1.8 cycle source, courtesy of bradfitz.
+	// TODO: Remove when (if?) idna package conforms to RFC 5895.
+	parsed.Host = width.Fold.String(parsed.Host)
+	parsed.Host = norm.NFC.String(parsed.Host)
+	if parsed.Host, err = idna.ToASCII(parsed.Host); err != nil {
+		return "", err
+	}
+
+	return NormalizeURL(parsed, f), nil
+}
+
+// NormalizeURL returns the normalized string.
+// It takes a parsed URL object as input, as well as the normalization flags.
+func NormalizeURL(u *url.URL, f NormalizationFlags) string {
+	for _, k := range flagsOrder {
+		if f&k == k {
+			flags[k](u)
+		}
+	}
+	return urlesc.Escape(u)
+}
+
+func lowercaseScheme(u *url.URL) {
+	if len(u.Scheme) > 0 {
+		u.Scheme = strings.ToLower(u.Scheme)
+	}
+}
+
+func lowercaseHost(u *url.URL) {
+	if len(u.Host) > 0 {
+		u.Host = strings.ToLower(u.Host)
+	}
+}
+
+func removeDefaultPort(u *url.URL) {
+	if len(u.Host) > 0 {
+		scheme := strings.ToLower(u.Scheme)
+		u.Host = rxPort.ReplaceAllStringFunc(u.Host, func(val string) string {
+			if (scheme == "http" && val == defaultHttpPort) || (scheme == "https" && val == defaultHttpsPort) {
+				return ""
+			}
+			return val
+		})
+	}
+}
+
+func removeTrailingSlash(u *url.URL) {
+	if l := len(u.Path); l > 0 {
+		if strings.HasSuffix(u.Path, "/") {
+			u.Path = u.Path[:l-1]
+		}
+	} else if l = len(u.Host); l > 0 {
+		if strings.HasSuffix(u.Host, "/") {
+			u.Host = u.Host[:l-1]
+		}
+	}
+}
+
+func addTrailingSlash(u *url.URL) {
+	if l := len(u.Path); l > 0 {
+		if !strings.HasSuffix(u.Path, "/") {
+			u.Path += "/"
+		}
+	} else if l = len(u.Host); l > 0 {
+		if !strings.HasSuffix(u.Host, "/") {
+			u.Host += "/"
+		}
+	}
+}
+
+func removeDotSegments(u *url.URL) {
+	if len(u.Path) > 0 {
+		var dotFree []string
+		var lastIsDot bool
+
+		sections := strings.Split(u.Path, "/")
+		for _, s := range sections {
+			if s == ".." {
+				if len(dotFree) > 0 {
+					dotFree = dotFree[:len(dotFree)-1]
+				}
+			} else if s != "." {
+				dotFree = append(dotFree, s)
+			}
+			lastIsDot = (s == "." || s == "..")
+		}
+		// Special case if host does not end with / and new path does not begin with /
+		u.Path = strings.Join(dotFree, "/")
+		if u.Host != "" && !strings.HasSuffix(u.Host, "/") && !strings.HasPrefix(u.Path, "/") {
+			u.Path = "/" + u.Path
+		}
+		// Special case if the last segment was a dot, make sure the path ends with a slash
+		if lastIsDot && !strings.HasSuffix(u.Path, "/") {
+			u.Path += "/"
+		}
+	}
+}
+
+func removeDirectoryIndex(u *url.URL) {
+	if len(u.Path) > 0 {
+		u.Path = rxDirIndex.ReplaceAllString(u.Path, "$1")
+	}
+}
+
+func removeFragment(u *url.URL) {
+	u.Fragment = ""
+}
+
+func forceHTTP(u *url.URL) {
+	if strings.ToLower(u.Scheme) == "https" {
+		u.Scheme = "http"
+	}
+}
+
+func removeDuplicateSlashes(u *url.URL) {
+	if len(u.Path) > 0 {
+		u.Path = rxDupSlashes.ReplaceAllString(u.Path, "/")
+	}
+}
+
+func removeWWW(u *url.URL) {
+	if len(u.Host) > 0 && strings.HasPrefix(strings.ToLower(u.Host), "www.") {
+		u.Host = u.Host[4:]
+	}
+}
+
+func addWWW(u *url.URL) {
+	if len(u.Host) > 0 && !strings.HasPrefix(strings.ToLower(u.Host), "www.") {
+		u.Host = "www." + u.Host
+	}
+}
+
+func sortQuery(u *url.URL) {
+	q := u.Query()
+
+	if len(q) > 0 {
+		arKeys := make([]string, len(q))
+		i := 0
+		for k, _ := range q {
+			arKeys[i] = k
+			i++
+		}
+		sort.Strings(arKeys)
+		buf := new(bytes.Buffer)
+		for _, k := range arKeys {
+			sort.Strings(q[k])
+			for _, v := range q[k] {
+				if buf.Len() > 0 {
+					buf.WriteRune('&')
+				}
+				buf.WriteString(fmt.Sprintf("%s=%s", k, urlesc.QueryEscape(v)))
+			}
+		}
+
+		// Rebuild the raw query string
+		u.RawQuery = buf.String()
+	}
+}
+
+func decodeDWORDHost(u *url.URL) {
+	if len(u.Host) > 0 {
+		if matches := rxDWORDHost.FindStringSubmatch(u.Host); len(matches) > 2 {
+			var parts [4]int64
+
+			dword, _ := strconv.ParseInt(matches[1], 10, 0)
+			for i, shift := range []uint{24, 16, 8, 0} {
+				parts[i] = dword >> shift & 0xFF
+			}
+			u.Host = fmt.Sprintf("%d.%d.%d.%d%s", parts[0], parts[1], parts[2], parts[3], matches[2])
+		}
+	}
+}
+
+func decodeOctalHost(u *url.URL) {
+	if len(u.Host) > 0 {
+		if matches := rxOctalHost.FindStringSubmatch(u.Host); len(matches) > 5 {
+			var parts [4]int64
+
+			for i := 1; i <= 4; i++ {
+				parts[i-1], _ = strconv.ParseInt(matches[i], 8, 0)
+			}
+			u.Host = fmt.Sprintf("%d.%d.%d.%d%s", parts[0], parts[1], parts[2], parts[3], matches[5])
+		}
+	}
+}
+
+func decodeHexHost(u *url.URL) {
+	if len(u.Host) > 0 {
+		if matches := rxHexHost.FindStringSubmatch(u.Host); len(matches) > 2 {
+			// Conversion is safe because of regex validation
+			parsed, _ := strconv.ParseInt(matches[1], 16, 0)
+			// Set host as DWORD (base 10) encoded host
+			u.Host = fmt.Sprintf("%d%s", parsed, matches[2])
+			// The rest is the same as decoding a DWORD host
+			decodeDWORDHost(u)
+		}
+	}
+}
+
+func removeUnncessaryHostDots(u *url.URL) {
+	if len(u.Host) > 0 {
+		if matches := rxHostDots.FindStringSubmatch(u.Host); len(matches) > 1 {
+			// Trim the leading and trailing dots
+			u.Host = strings.Trim(matches[1], ".")
+			if len(matches) > 2 {
+				u.Host += matches[2]
+			}
+		}
+	}
+}
+
+func removeEmptyPortSeparator(u *url.URL) {
+	if len(u.Host) > 0 {
+		u.Host = rxEmptyPort.ReplaceAllString(u.Host, "")
+	}
+}