User supplied music support!

D2X-XL now supports user supplied music (mp3 or ogg/vorbis). You can specify a song to be played in the menus and a playlist giving the level songs. D2X-XL will cycle through the level songs, playing one song per level and repeating it if necessary until the level is finished.

Currently this only works on Windows, but Linux and (hopefully) OS X will follow soon.