xP: implement tab completion

Currently it only goes for the longest common prefix.

Refactor WebSocket handling into an abstraction for our protocol.

The Go code generater finally needed fixing.

xC-gen-proto-go.awk

@@ -382,7 +382,8 @@ function codegen_union(name, cg,    gotype, tagfield, tagvar) {
 	print "}"
 	print ""
 
-	print "func (u *" gotype ") MarshalJSON() ([]byte, error) {"
+	# This cannot be a pointer method, it wouldn't work recursively.
+	print "func (u " gotype ") MarshalJSON() ([]byte, error) {"
 	print "\treturn json.Marshal(u.Interface)"
 	print "}"
 	print ""