Implemented some sceMp3 functions

I have started work on implementing the sceMp3 functions. It's probably a bit unstable right now (though I have tested it with Aqua Panic, and a test eboot I made and they both seem to work). 
Currently it doesn't do any decoding at all, but it should be quite easy to add if we use an external mp3 library.

If you have DEBUG set it'll output the buffered mp3 data as separate files to the current directory.