Spinach

- Fix typo preventing the Django/Datadog integration from starting

- Automatically detect dead workers (killed processes, power outage...) and re-enqueue the jobs that were running on them.
- Fix a bug that could result in jobs not being retried if they finished while the workers were shutting down.
- Fix the integration between Django, Datadog and Spinach. Users of these three libraries may have seen the Datadog integration not reporting tasks anymore.
- Remove the deprecated Raven integration, users are encouraged to use the Sentry SDK integration instead.
- Enable performance tracing of tasks with the Sentry SDK.

- Provide a traceback when logging retry warnings
- Prevent jobs with incompatible task arguments from being scheduled

- Add `AbortException` to stop a job from being retried
- Add new Sentry SDK integration
- Deprecate old Sentry Raven integration

- Allow to safely retry enqueuing jobs
- Use a single Lua script to enqueue normal and future jobs: make scheduling a batch truly atomic
- Add Datadog APM integration

- Switch back to sending signals from worker threads
- Allow to schedule a task using its function