Hirefire

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- Remove an annoying warning (57)
- Output request queue time for Django (55)

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- Make RQ proc counting more efficient and correct (49)
- CeleryProc close open channels (51)

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- Make ProcSerializer inherit from object (47)

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- Use concurrent futures to reduce blocking IO (37)
- Add a test suite (41)
- Fix RabbitMQ connection `TimeoutError` (42).
Acquire and dispose broker connection per request

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- Add ``simple_queues`` feature to Celery Proc, to enable optionally
skipping one inspect call. (23)
- Make the default quantity 0 by the recommendation of the HireFire team.

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- Consider all Celery tasks including the ones in the active, reserved and
scheduled queues. This fixes a long standing issue where tasks in those
queues could have been dropped if HireFire were to scale down the workers.
Many thanks to Ryan Hiebert for working on this.

- Removed django-pq backend since the library is unmaintained.