Combine forwards events to a list of ackers.

ConnectionOnly ensures that the given ACKer is only used for as long as the pipeline Client is active.

Counting returns an ACK count for all events a client has tried to publish.

EventPrivateReporter reports all private fields from all events that have been published or removed.

LastEventPrivateReporter reports only the 'latest' published and acked event if a batch of events have been ACKed.

Nil creates an ACKer that does nothing.

RawCounting reports the number of ACKed events as has been reported by the outputs or queue.

TrackingCounter keeps track of published and dropped events.