Load an unlimited amount of loose music

[NyakoFox]

Changes:

Binary blobs can now store 128 tracks, and music can now be read from loose files. Unfortunately, the two cannot be used together -- loose music can still only use 16 tracks. This commit attempts to fix that, allowing for music playback by filename.

Closes #965.

Legal Stuff:

By submitting this pull request, I confirm that...

• [x] My changes may be used in a future commercial release of VVVVVV
• [x] I will be credited in a CONTRIBUTORS file and the "GitHub Friends" section of the credits for all of said releases, but will NOT be compensated for these changes unless there is a prior written agreement

[NyakoFox]

todo: on line 383 of music.cpp, needs a SDL_strdup(name) instead of just name