Merge pull request #108 from seomoz/add_max_concurrency

Add max concurrency
Update qless-core.
Don't blow up when max_concurrency hasn't been set yet.
Fix a typo in the README
Fix the worker so it does not leak threads.

Previously, it would start a subscriber thread every time `work`
was called and then leave it running.
Merge pull request #117 from seomoz/stop_thread_leakage

Fix the worker so it does not leak threads.
Merge branch 'master' into kill_exhausted_retries_error

Conflicts:
	lib/qless/qless-core