go: re-do the entire thing

This is a mega-change, but attempting to split this up further is
probably not worth the effort.

Summary:

1. Bump up bazel, rules_go, and others.
2. Switch to new go target naming (bye bye go_default_library)
3. Move go deps to go.mod/go.sum, use make gazelle generate from that
4. Bump up Python deps a bit

And also whatever was required to actually get things to work - loads of
small useless changes.

Tested to work on NixOS and Ubuntu 20.04:

   $ bazel build //...
   $ bazel test //...

Change-Id: I8364bdaa1406b9ae4d0385a6b607f3e7989f98a9
Reviewed-on: https://gerrit.hackerspace.pl/c/hscloud/+/1583
Reviewed-by: q3k <q3k@hackerspace.pl>
diff --git a/devtools/hackdoc/markdown.go b/devtools/hackdoc/markdown.go
index a6f206d..1557af1 100644
--- a/devtools/hackdoc/markdown.go
+++ b/devtools/hackdoc/markdown.go
@@ -10,7 +10,7 @@
 
 	"github.com/gabriel-vasile/mimetype"
 	"github.com/golang/glog"
-	"gopkg.in/russross/blackfriday.v2"
+	"github.com/russross/blackfriday/v2"
 )
 
 // renderMarkdown renders markdown to HTML, replacing all relative (intra-hackdoc) links with version that have ref set.