Add doc comments to sdl_mixer.go, make func names consistent
Add doc comments to sdl_mixer.go, make func names consistent

krux02/go-sdl2,krux02/go-sdl2,krux02/go-sdl2,jangler/go-sdl2,phicode/go-sdl2,phicode/go-sdl2,veandco/go-sdl2,jangler/go-sdl2,jangler/go-sdl2,phicode/go-sdl2,veandco/go-sdl2