Thomas de Zeeuw

Pr #330 collects some metrics, but it's closed.

Also see https://github.com/Thomasdezeeuw/heph/issues/31#issuecomment-734459185.

PR #462 implements some metrics, but they're just dumped out currently.

Some more metrics I want to monitor: Memory usage: * Heap size * Usage per worker/coordinator. Per actor: * name * supervisor (?) * inbox/message queue size * priority *...

My current idea/prototype is using a single thread-safe/sync actor to handle the connection to the backend/database and relay requests to it using an `ActorRef`.

Pr #429 removes the lock from the `Inactive` tree, now the `RunQueue` is left.

This should be resolved when fixing #284.

Fixed in #423.

Reopened by commit e8c0e158c838f04e1b402e7e3f904520e724d819.

Some context: `Spawn` should be able to be used in functions that start actors. For example: ```rust fn start_my_actor(spawn: S) where S: Spawn { // ... } ``` The problem...