docs: function unsubscribe(event, callback) {
  	/*jshint validthis: true */
  	if (DEBUG_DISPATCHER) log.info('UNSUBSCRIBE: ' + event);
  	if (!event || !callback) {
  		return;
  	}
  	var callbacks = this._callbacks[event];
  	if (callbacks) {
  		for (var i = callbacks.length - 1; i >= 0; i--) {
  			if (callbacks[i] === callback) {
  				callbacks.splice(i, 1);
  			}
  		}
  	}
  
  	if (!callbacks || callbacks.length === 0) {
  		this._client.unsubscribe(event);
  	}
  
  	return this;
  }