mode7 speed fixes:

	+  Skip key parsing if no key read

	+ Self modifying code on the adds in inner loop

	+ inline lookup_map (or at least a copy of it)
		maybe code that detects if spacex/spacey add
		incremented and just skip the lookup (avoid the need
		for the cache code)

	+ Unroll inner loop?  Might not help much since we are 
		self-modifying and would have to duplicate
		that.


short term:

longer term:
	sky -- color looks too much like grass on monochrome display
	map -- adjust x/y to better match real position
	name entry screen
	inventory screen
	collision detection
	after game over, return to title screen
	save/restore game


