message: Updated. use Reference dsl
diff: @@ -11,6 +11,8 @@ var UserMediaType = MediaType("application/vnd.user+json", func() {
  Description("A User")
  ContentType("application/json")
  + Reference(UserPayload)
  +
  Attributes(func() {
  Attribute("id", Integer, "id")
  Attribute("name", String, "user name")
  