Merge pull request #14 from sulix/master

SDL_mouse.h
SDL_audio paaaart oooone
Quick compile fix, SDL_audio paaaaart twoooooish
Yet another build fix, so many margfargling keywords
SDL_audio implemented. Function pointers are a concern here.
Forgot to take out the Audio TODO. Not my morning, is it?
Keep it in order according to the APIByCategory page.
Audio CVT cannot be supported in C#, SDL_AudioCallback might work though.
Made some struct members public