Pyramid-tasks

- Add `CeleryWorkerProcessInit` event.

- Replace task tweens with task derivers. (Backwards incompatible)
- Rename `delay_task` to `defer_task`.
- Add `request.defer_task_with_options`.
- Add `BeforeDeferTask` event.

- Add support for Python 3.10.
- Documentation fix.

Fix argument order for task derivers.

First alpha for the 0.3 line.

* Replace task tweens with task derivers.
* Rename `delay_task` to `defer_task`
* Add `request.defer_task_with_options`
* Add `BeforeDeferTask` event

Pyramid 2 support.