* Attempt to fix hmset command for Redis < 4.0

* Temporarily commented out hset(key, mapping) for backward compatibility reasons.

* First RQScheduler prototype

* WIP job scheduling

* Fixed Python 2.7 tests

* Added ScheduledJobRegistry.get_scheduled_time(job)

* WIP on scheduler's threading mechanism

* Fixed test errors

* Changed scheduler.acquire_locks() to instance method

* Added scheduler.prepare_registries()

* Somewhat working implementation of RQ scheduler

* Only call stop_scheduler if there's a scheduler present

* Use OSError rather than ProcessLookupError for PyPy compatibility

* Added `auto_start` argument to scheduler.acquire_locks()

* Make RQScheduler play better with timezone

* Fixed test error

* Added --with-scheduler flag to rq worker CLI

* Fix tests on Python 2.x

* More Python 2 fixes

* Only call `scheduler.start` if worker is run in non burst mode

* Fixed an issue where running worker with scheduler would fail sometimes

* Make `worker.stop_scheduler()` more resilient to errors

* worker.dequeue_job_and_maintain_ttl() should also periodically run maintenance tasks

* Scheduler can now work with worker in both burst and non burst mode

* Fixed scheduler logging message

* Always log scheduler errors when running

* Improve scheduler error logging message

* Removed testing code

* Scheduler should periodically try to acquire locks for other queues it doesn't have

* Added tests for scheduler.should_reacquire_locks

* Added queue.enqueue_in()

* Fixes queue.enqueue_in() in Python 2.7

* First stab at documenting job scheduling

* Remove unused methods

* Remove Python 2.6 logging compatibility code

* Remove more unused imports

* Added convenience methods to access job registries from queue

* Added test for worker.run_maintenance_tasks()

* Simplify worker.queue_names() and worker.queue_keys()

* Updated changelog to mention RQ's new job scheduling mechanism.

* modify zadd calls for redis-py 3.0

redis-py 3.0 changes the zadd interface that accepts a single
mapping argument that is expected to be a dict.
https://github.com/andymccurdy/redis-py#mset-msetnx-and-zadd

* change FailedQueue.push_job_id to always push a str

redis-py 3.0 does not attempt to cast values to str and is left
to the user.

* remove Redis connection patching

Since in redis-py 3.0, Redis == StrictRedis class, we no longer
need to patch _zadd and other methods.
Ref: https://github.com/rq/rq/pull/1016#issuecomment-441010847

* Solve the UnicodeDecodeError while decode literal things.

* Add test case for when worker result is a unicode or str object that other than
pure ascii content.

This has been discussed in #514, #282 and #88.

Using an explicit type check via `isinstance`, rather than duck typing, is typically considered unpythonic and breaks compatibility with mock objects such as FakeRedis. This patches removes the type check, and instead looks for a common method that should be present on the object as a hint on whether it's compatible or not.