Added purge (aka async_flush) functionality

[accelerated]

Added asynchronous flush capability.

[accelerated]

If you can merge this that would be great! Cheers!

[mfontanini]

I really thought I had merged this one, sorry :(. Anyway, I imagine you wanted the other one merged first so I went for that one.

[accelerated]

Before I resolve the conflicts, I actually had one question for you...i was debating if purge was the right name here or perhaps async_flush. Do you have any preferences? I think async_flush is easier to understand what it does, but there there's produce and sync_produce so people might wonder why intermixing sync and async as it's not consistent.

[mfontanini]

True, "purge" maybe sounds like you're getting rid of the messages rather than sending them. I'm not great at naming things but I think async_flush could work. I can't think of any other names... This is like some sort of "light flush" but that doesn't sound right.

[accelerated]

ok cool, I'll change the name and push the update in a few mins.

[accelerated]

Done!

[mfontanini]

Thanks!