[Audio] Implement sndio audio backend

[f1nalspace]

Implement a audio backend for sndio: https://sndio.org/

[KungPhoo]

II don't know if you need this specific library, but I had great success with https://github.com/mackron/miniaudio in combination with https://github.com/jarikomppa/soloud.

[f1nalspace]

Not really the point of that issue, but if you need sndio support - right now, miniaudio or others are your only option.
However, OSS works great which i tested in a FreeBSD system without any issues.

Btw, FPL does not use any third party libraries at all, but the very first draft of the audio system that i created in 2018 was inspired by the miniAL architecture (predecessor of miniaudio).

However miniaudio is a great library!

If you need more audio capabilities, just use miniaudio and disable audio in FPL entirely.