Threshold for queued/retry items and bug fixes

FIX - check retry queue(scheduled) which was not checked before, when no worker is active
FIX - fix worker sorting when more than 9 workers are present (worker.1, worker.10, worker.2, ..., worker.9)

NEW - add threshold (default 20 seconds) when checking for scheduled and retry jobs (so that it wont add a worker when no workers are active for jobs that will not be run soonish)

Improve configuration

Do not raise exception on invalid configuration

First release

v0.1.0

Add spec files