Spinach

- Add Flask integration
- Add Django integration
- Terminate blocking workers on SIGTERM
- Start worker thread name at 1 instead of 0

- Prevent worker thread from dying during callback in case of connection error to redis
- Officially support Python 3.7
- Reset periodic task score when periodicity is changed
- Add option to stop workers when their queue is empty
- Remove useless function wrapper in decorator
- Submit job execution results to broker from a single thread
- Only generate as many UUIDs as there are periodic tasks
- Log information about workers on startup

* Automatically schedule periodic tasks

* Keep track of running idempotent jobs
* Add job_failed and job_schedule_retry signals
* Add Sentry integration
* Arguments passed to signal handlers are not copied anymore
* Rename Spinach class to Engine
* Allow to retry jobs with RetryException
* Make Spinach more reliable to connection errors
* Handle receiving unknown tasks
* Allow to schedule jobs in batch
* Allow to define tasks in the Engine directly

* Prevent user from using queues starting with '_'
* Add ability to flush a broker
* Move Redis broker code into the broker package
* Implement signals: Spinach sends signals when some events happen
* Allow to retry failed jobs
* Allow to schedule jobs from a Tasks object

Fix distribution