Audio API rework

[fredi-68]

Now that we are using a custom audio engine, this should not be too bad. At least we only have to update that and not the entire codebase that uses it. However, I believe the new audio system discord.py is going to ship with may be functionally close enough to my implementation that we can offload most of the work onto that. Will need to check the specifics once it has been implemented and finalized.

[fredi-68]

This patch has been in testing for quite a while and is now considered stable. The only remaining issue is some audio artifacting sometimes occurring at the end of a sound, thought I am still unsure what is causing this.