code: function (events, handler) {
      var handlers = this.handlers;
      splitStr(events).forEach(function (event) {
        if (!handler) {
          delete handlers[event];
        } else {
          handlers[event].splice(handlers[event].indexOf(handler), 1);
        }
      });
      return this;
    }
docs: unbind event, leave emit blank to remove all handlers
  @param {String} events
  @param {Function} [handler]
  @returns {EventEmitter} this