title
~~~~~
	+ menu
	+ load/save game
	+ credits?

mars map
~~~~~~~~
	+ make tiles for first level and green level impassable
	+ animate stars
	+ enforce collision detection
	+ proper smooth movement
	+ show keens left at start, also when press ??
	+ mark completed levels
		at start, over-write finished levels with blue tiles
		check completed levels when action and not let you re-enter
level engine
~~~~~~~~~~~~~
	+ make generic

sound effects
~~~~~~~~~~~~~


movement:
~~~~~~~~~
	+ scroll with sub-block movement?  might not work at hi-res?

enemies
~~~~~~~
	+ disable when not on screen?
	+ enemies besides yorps

shooting
~~~~~~~~
	+ FIX collision with enemies
	+ shoot enemies

pogo
~~~~
	+ implement


lo-res version
~~~~~~~~~~~~~~
+ improve keyboard handling on Apple IIe
+ walk behind some sprites (columns on level1)
+ better animations
+ game over screen if out of lives

hi-res version
~~~~~~~~~~~~~~
+