message: Add get_menu
diff: @@ -452,6 +452,9 @@ function Facebookbot(configuration) {
  delete_menu: function () {
  facebook_botkit.api.messenger_profile.deleteAPI('persistent_menu');
  },
  + get_menu: function (cb) {
  + facebook_botkit.api.messenger_profile.getAPI('persistent_menu', cb);
  + },
  account_linking: function (payload) {
  var message = {
  'account_linking_url': payload
  