Features:
* follow the playlist progression as items are played
* the --dev option enable debug logs
Internals:
* use [Hypercorn](https://pgjones.gitlab.io/hypercorn/) instead of Uvicorn as Uvicorn does not let us specify the event loop
* a lot of routes are now asynchronous
* start an async loop at app startup to listen for MPV events
* connect to MPV on startup, do not wait for first request anymore
* add some logs, mostly related to the Player and MPV management