Some prettier backend stuff

NOT TESTED

DO NOT MERGE YET
Pretty Mutex Work, Tests

Because everybody needs good tests
Added a hell of a lot of documentation

Focusing on wav_head_player for now.
More docs for ConstantlySortedQueue
Lots of Docs for WavHead::Info
Docs for WavHead::ArtParser
Made sure everything works

And, when it didn't, fixed it.
Merge pull request #57 from noidedmedia/backend-cleanup

Backend cleanup