Memory map:
	$0000-$00ff = zero page
	$0100-$01ff = stack
	$0200-$03ff = ???
	$0400-$07ff = lo-res page1
	$0800-$0bff = lo-res page2
	$0c00-$0fff = background image
	$1000-$1fff = loader
	$2000-$3fff = code		(8k? currently 5k)

	; MARS = 6k
	; LEVEL1 = 6k
	; TITLE  = 4k

	; LOAD engine at $4000
	; $4000 - $5fff = 8k worst case
	; LOAD level data at $6000
	; $6000 - $7fff = 8k worst case

	$9000-$93FF = tiles		(1k)
	$9400-$BBFF = big_tilemap	(10k)  128x80
	$BC00-$BCFF = small tilemap	(256B) 20x12 

tiles are 2x4, or 4 bytes each
	so in theory can have up to 256 of them
	but if we want data to fit in one page then 64 it the maximum

tilemap:
	tilemap is 256 wide by 40 tall = 10k

Tile types:
	 0..26 transparent tiles
	27..31 items
	32..39 walkthrough tiles
	40..63 hard tiles


Status:

0123456789012345678901234567890123456789
****************************************
* KK KK KK KK KK KK * RR  YY *         *
* KK KK KK KK KK KK * RR  YY *         *
* KK KK KK KK KK KK * BB  GG *         *
* KK KK KK KK KK KK * BB  GG *         *
****************************************
* KEENS              KEYCARDS   PARTS  *
****************************************
*  SCORE   * NEXT KEEN * RAYGUN  * POGO*
* 33221100 *     20000 *   5     *  N  *

score always multiple of 100


Level1:
	in png: X=80 to 543,	Y=12 to 80	(tiles 4x4)
		x=0 to 116	Y=0..17

	start position: in png 88,65
		tile position = 0,5
		keen position = 2,24 (remember, tiles 2 bytes high)

	tilemap copies 



TILEMAP_X
TILEMAP_Y
KEEN_X / KEEN_XL
KEEN_Y



Enemy logic:
	when update tilemap
		detect if enemy on screen
		if so mark active
		give it current x/y value
		
	when move
		same as keen move
		if move off left/right side of screen mark inactive