Music Player

I've added a Config menu implementation. The music player can be accessed by pressing A or Right. I also fully commented both implementations. Music player data and code are now in separated ASM files to ease editing and getting rid of code repetitions. However the core music player ASM file is not yet commented. To implement one of the two options assemble with xkas 0.06 either ff6_music_config.asm or ff6_music_main.asm. Both implementations use the same player core and data file (song names, pointers and list).