def on(name, *args, &block)
      $bot[:callbacks][name] ||= []
      $bot[:callbacks][name] << {
          args: args,
          block: block
      }
    end
def on(name, *args, &block)
      $bot[:callbacks][name] ||= []
      $bot[:callbacks][name] << {
          args: args,
          block: block
      }
    end
@param name [Symbol] The name of the botpart.  Should be the same as the file name without the extension.
 Adds a new callback to +name+.
 @param name [Symbol] The callback type.
   Can be one of:

   * :tweet
   * :mention
   * :retweet
   * :favorite
   * :friend_list
   * :direct_message (i.e. not command DMs, see {cmd} for that)
   * :load (when the bot finished initializing)
   * :deleted (when a tweet got deleted, only stores id in object)