SDL_mixer docs : update

Two functions added, the docs are considered complete. If you see a function or typedef missing or any other errors, please email me.

Also added a simple wav display demo. There is only one more demo on my queue, so more recommendations are welcome.

here’s the URL for all that stuff:

http://jcatki.2y.net/SDL_mixer/-- 
          -=<Long Island Man>=-
                Jon Atkins
          http://jcatki.2y.net/