Add limit on messages pending resend

[philipwhiuk]

Fixed #477

[chrjohn]

Hi @philipwhiuk , I've just merged #380 .
So it should be a matter of creating your own queue implementation with an enqueue method similar to this:

public void enqueue(int sequence, Message message) {
    if (backingMap.size() < maxMessagesQueuedWhilePendingResend || maxMessagesQueuedWhilePendingResend == -1) {
        backingMap.put(sequence, message);
    }
}

Do you think it is OK to close this PR then? Would you like to submit a PR with a queue implementation that is limited in size?
Thanks,
Chris.

[philipwhiuk]

Hi Chris, Yeah, I'll look at creating a PR for this.