hswaw/smsgw: implement

The SMS gateway service allows consumers to subscribe to SMS messages
received by a Twilio phone number.

This is useful for receiving SMS auth messages.

Change-Id: Ib02a4306ad0d856dd10c7ca9241d9163809e7084
diff --git a/hswaw/smsgw/proto/smsgw.proto b/hswaw/smsgw/proto/smsgw.proto
new file mode 100644
index 0000000..2a95308
--- /dev/null
+++ b/hswaw/smsgw/proto/smsgw.proto
@@ -0,0 +1,17 @@
+syntax = "proto3";
+package proto;
+option go_package = "code.hackerspace.pl/hscloud/hswaw/smsgw/proto";
+
+message MessagesRequest {
+    string filter_body = 1;
+}
+
+message MessagesResponse {
+    string sender = 1;
+    string body = 3;
+    int64 timestamp = 4;
+}
+
+service SMSGateway {
+    rpc Messages(MessagesRequest) returns (stream MessagesResponse);
+}