* Initial implementation of Retry class
* Fixes job.refresh() under Python 3.5
* Remove the use of text_type in job.py
* Retry can be scheduled
* monitor_work_horse() should call handle_job_failure() with queue argument.
* Flake8 fixes
* Added docs for job retries
* add doc page for job registries
* Use consistent language in registry type descriptions
* Correct usage of 'connection' parameter in Job Registry doc