Partial Apple II port (40-column only)

I haven't run the other versions, so I'm a little unsure of what the game is supposed to do regarding enemies.  I may have some issues there.  Also there's a weird anomaly with the score/air display on occasion. 

Other than that, it seems to work fine. 

I'll go back and try to clean this up a bit and fix bugs, but I thought I'd at least try to put this one out there so there's a starting point for anyone else wanting to do an Apple II version.