Major refactor + FileQueue

Add before_fn and after_fn to poll. Remove log_fn.

Progress bars for MockTaskQueue.

fix multiprocessing progress bar

Elapsed time in task completion message.

Make LocalTaskQueue work like MockTaskQueue for insert_all.

Multiprocessing supports dynamic class iterators.

Export QueueEmpty

Parallel option for insert_all

Batching, Green Threads, LocalTaskQueue fixes, documentation update