Simple tool to convert PNG files with a palette to 4 or 16 colour SNES
tiles.  It currently only supports 8x8 tiles.

Usage: snesgfx [-p palette_file] [-s] [-c colours] source.png dest.data

-p palette_file	Write a SNES palette based on the one in the image to the
		passed file.
-s		Indicates 16x16 tiles.  Currently unsupported.
-c colours	Colours -- either 4 or 16.  Defaults to 4.
source.png	The source PNG file.
dest.data	Where to write the SNES tile data.