Working Item System and Decompression

You can now equip weapons and pick up gold and maps across the terrain. Additionally, the items have some basic artwork; however, when I transition to 16x16 metasprites, they'll all change.

Enemies will be coming next!

I also enabled cross-compiling to all the systems GBDK supports. I'll only be testing .gb, though, so the other ROMs are just in case.