Added LoadWAV, PlayChannel and Free for handling Chunks.

Found out that you only can play one piece of music at a time, so I couldn't finish this tutorial properly:

http://lazyfoo.net/SDL_tutorials/lesson11/index.php

Wasn't that hard to include, hope that there are not copy&paste errors.

P.S.: annoying to change the import paths everytime for developement from [...]/0xe2-0x9a-0x9b/Go-SDL/[...] to [...]/pakohan/Go-SDL/[...] and vice versa.