AHX tracker file format support

[LambdaCalculus]

I've returned from the abyss, it seems! I can never stay away from Rockbox! 

In the time I've been away, I've been discovering new things, including new formats for module files, thanks to my newfound passion for Amiga computers!

One I've been looking at and have started using quite a bit are AHX tracker files, which are synth-tracker files that don't contain samples like other tracker formats do (e.g. MOD, MED, XM, IT, etc.), but instead only contain descriptors for synthesizing the necessary sounds. This allows AHX files to be significantly smaller (usually anywhere from a few hundred bytes to around 5K per track), and the format gives a unique, chiptune-ish sound.

While several players do exist for various OSes, and several other players like Audacious do (or might) support them, I'm still looking for one that is properly GPL'ed so that it may be able to be implemented into Rockbox as a codec.

There is some information about the AHX format and its internal structure here, for those who may be a little curious: http://lclevy.free.fr/exotica/ahx/ahxformat.txt

If anyone wants to download some AHX files to explore them, Aminet is a good source!