snes: Start adding some sprite code

This includes some common sprite clearing code in svmwgraph
snes: fix sprite copy routine

urgh the 8/16 bit rep/sep strikes again
snes: remove pcx_to_sprite tool

We'll just use the pcx to 4bpp tile tool instead
snes: pcx_to_tiles_4bpp

clean up code, add command line argument for label name
snes: pcx_to_tiles_4bpp

forgot to actually add the command-line parsing code
snes: sprite displaying properly!

Looks nice