Server with systemd service integration

[hasezoey]

Having the server running as a service would likely be good to be available in some cases.
We could just do a plain service with the current state of termusic, but there are some things i would likely to change / implement for going for a full integration:

Service features:

• Provide a pre-made .service file
• Reload config on SIGHUP?
• Setting state via sd_notify (starting, started, exiting)
• Socket-activate-able; use the socket provided by the service on start (FDSTORE?) instead of opening one ourself

Points mainly taken from Systemd: daemon (re New-Style Daemons)

Refactors that should likely happen before then:

• Quitting to be a RPC call instead of platform-dependant signal (and let the server decide if it wants to quit or not)
• Playlist fast-start (re Potential slow open with large playlist.log and slow backing storage #493)

[tramhao]

Please note one thing, currently termusic is working on windows and perhaps macos too. System specific features could harm the experience in other platforms.

[hasezoey]

System specific features could harm the experience in other platforms.

I dont think it would impact them as this would be first target-gated, then very likely also feature gated.

Windows also has services, but i have no experience with them, so that could also be added at some point.

[tramhao]

Make sense:)