code: function(evname, callback, context) {
      if (!evname && !callback && !context) {
        this._events = {};
        return this;
      } else if (!evname) {
        for (var _evname in this._events) {
          this.off(_evname, callback, context);
        }
        return this;
      } else {
        var fns = this._events[evname], l = fns.length;
        while (l--) {
          if ((callback ? fns[l].cb === callback : true) && (context ? fns[l].ctxt === context : true)) {
            fns.splice(l, 1);
          }
        }
        return this;
      }
    }
docs: Remove event listener
  
  @param {string} name of event
  @param {function} callback if event is triggered
  @return {this}