* Add diesel feature
This can simplify Lemmy code and avoid converting back and forth
to DbUrl type all the time.
* Also add diesel derives for CollectionId
* Add ObjectId::dereference_forced
* no deprecated code
* fmt
* Remove `actix-rt` and replace with tokio tasks
* Include activity queue test
* Use older `Arc` method
* Refactor to not re-process PEM data on each request
* Add retry queue and spawn tokio tasks directly
* Fix doc error
* Remove semaphore and use join set for backpressure
* Fix debug issue with multiple mailboxes