code: func (s *Service) UnsubscribeMultiple(topics []string) GenericFuture {
  	s.mutex.Lock()
  	defer s.mutex.Unlock()
  
  	// remove subscription
  	for _, v := range topics {
  		s.subscriptions.Empty(v)
  	}
  
  	// allocate future
  	f := future.New()
  
  	// queue unsubscribe
  	s.commandQueue <- &command{
  		unsubscribe: true,
  		future:      f,
  		topics:      topics,
  	}
  
  	return f
  }
docs: // UnsubscribeMultiple will send a Unsubscribe packet containing multiple
  // topics to unsubscribe. It will return a SubscribeFuture that gets completed
  // once the acknowledgements have been received.