code: func (ch *Channel) Ack(tag uint64, multiple bool) error {
  	ch.m.Lock()
  	defer ch.m.Unlock()
  
  	return ch.send(&basicAck{
  		DeliveryTag: tag,
  		Multiple:    multiple,
  	})
  }
docs: /*
  Ack acknowledges a delivery by its delivery tag when having been consumed with
  Channel.Consume or Channel.Get.
  
  Ack acknowledges all message received prior to the delivery tag when multiple
  is true.
  
  See also Delivery.Ack
  */