Rq

* Added `job.worker_name` attribute that tells you which worker is executing a job. Thanks selwin!
* Added `send_stop_job_command()` that tells a worker to stop executing a job. Thanks selwin!
* Added `JSONSerializer` as an alternative to the default `pickle` based serializer. Thanks JackBoreczky!
* Fixes `RQScheduler` running on Redis with `ssl=True`. Thanks BobReid!

* Worker now properly releases scheduler lock when run in burst mode. Thanks selwin!

* Workers now listen to external commands via pubsub. The first two features taking advantage of this infrastructure are `send_shutdown_command()` and `send_kill_horse_command()`. Thanks selwin!
* Added `job.last_heartbeat` property that's periodically updated when job is running. Thanks theambient!
* Now horses are killed by their parent group. This helps in cleanly killing all related processes if job uses multiprocessing. Thanks theambient!
* Fixed scheduler usage with Redis connections that uses custom parser classes. Thanks selwin!
* Scheduler now enqueue jobs in batches to prevent lock timeouts. Thanks nikkonrom!
* Scheduler now follows RQ worker's logging configuration. Thanks christopher-dG!

* Scheduler now uses the class of connection that's used. Thanks pacahon!
* Fixes a bug that puts retried jobs in `FailedJobRegistry`. Thanks selwin!
* Fixed a deprecated import. Thanks elmaghallawy!

* Fixes for Redis server version parsing. Thanks selwin!
* Retries can now be set through job decorator. Thanks nerok!
* Log messages below logging.ERROR is now sent to stdout. Thanks selwin!
* Better logger name for RQScheduler. Thanks atainter!
* Better handling of exceptions thrown by horses. Thanks theambient!

* Failed jobs can now be retried. Thanks selwin!
* Fixed scheduler on Python > 3.8.0. Thanks selwin!
* RQ is now aware of which version of Redis server it's running on. Thanks aparcar!
* RQ now uses `hset()` on redis-py >= 3.5.0. Thanks aparcar!
* Fix incorrect worker timeout calculation in SimpleWorker.execute_job(). Thanks davidmurray!
* Make horse handling logic more robust. Thanks wevsty!