rpc generation fix (#184)

* reactor alert

* optimize

* add test case

* update the target directory in case proto contains option

* fix missing comments and format code

tools/goctl/rpc/parser/comment.go

@@ -6,5 +6,5 @@ func GetComment(comment *proto.Comment) string {
 	if comment == nil {
 		return ""
 	}
-	return comment.Message()
+	return "// " + comment.Message()
 }