code: function(name, callback) {
        this._events = this._events || {};
        var token = _.uniqueId('t');
        return this.subscribe(name, function() {
          this.unsubscribe(name, { token : token });
          callback.apply(this, arguments);
        }, this, token);
      }
docs: Allows subscribing to an event once. When the event is triggered
  this subscription will be removed.
  Params:
  name - name of event
  callback - The callback to trigger