Adding LeafGreen

I copied and then changed all files to allow the system to (hopefully) work with LeafGreen. Most  of it isn't changed, and what is, is mostly offsets in the various files. I didn't test it, but it looks like it will work.

Also, all code applying to LeafGreen has "-lg" added to the file name (if it wasn't obvious).

I think this might be an error, but iirc Leaf Green's game code is BPGE, so this might need fixing in order for it to work proper when compiling via make.