code: function handler(notification) {
          debug('summoner received a mention notification!');
          return notification.getUser()
              .then((user) => {
                  debug(`summoner responding to summons by ${user.name}`);
                  const index = Math.floor(Math.random() * messages.length);
                  const message = messages[index].replace(/%(\w+)%/g, (_, key) => {
                      let value = user[key];
                      if (key === 'name' && !value) {
                          value = user.username;
                      }
                      value = value || `%${key}%`;
                      if (typeof value !== 'string') {
                          value = `%${key}%`;
                      }
                      return value;
                  });
                  debug(`summoner replying with: ${message}`);
                  return forum.Post.reply(notification.topicId, notification.postId, message);
              }).catch((err) => {
                  forum.emit('error', err);
                  return Promise.reject(err);
              });
      }
docs: Handle a mention notification.
  
  Choose a random message and reply with it
  
  @param {Notification} notification Notification event to handle
  @returns {Promise} Resolves when event is processed