Merge pull request #622 from ardell/master

Fix #621 fix job re-queueing on hard shutdown (e.g. SIGTERM).
Push to front of queue, not back
Update changes, bump version
Explicate the ruby version
Batch process worker removal for performance. #623
Improve efficiency and reliability of re-queueing when workers are terminated. #623
Clear workers in redis before terminating worker threads. #623