message: allow realm and user args to be optional
diff: @@ -42,7 +42,7 @@ struct user_options
  {
  std::string username;
  std::string password;
  - std::string realm;
  + user_optional<std::string> realm;
  user_optional<std::string> addr;
  user_optional<std::string> port;
  @@ -275,9 +275,6 @@ static void process_options(int argc, char** argv)
  if (not uri_check.is_strict_uri(i.c_str()))
  die("not strict uri: " + i);
  }
  -
  - if (uopts.username.empty()) die("missing username");
  - if (uopts.realm.empty()) die("missing realm");
  }
  std::string get_timestamp()
  @@ -387,7 +384,7 @@ int main_impl(int argc, char** argv)
  throw std::runtime_error("failed to obtain wamp session");
  wampcc::client_credentials credentials;
  - credentials.realm = uopts.realm;
  + credentials.realm = uopts.realm? uopts.realm.value() : "default_realm";
  credentials.authid = uopts.username;
  credentials.authmethods = {"wampcra"};
  credentials.secret_fn = [=]() -> std::string { return uopts.password; };
  