lep: request all the things

I'm experimenting with a new API to allow queue's of work to be done, where the callback of each queue returns an `int`. If the return value is `!= 0` then the queue stops being processed. With that, I'd probably have to add a queue complete callback.

Anyway, I got part of the idea from GCD and I'll be implementing it in libnub for testing. This is just an FYI.