Memory Map:
	$0000-$0100 = ZERO PAGE
	$0100-$0200 = STACK
	$0400-$0800 = TEXT/GR PAGE0
	$0800-$0C00 = TEXT/GR PAGE1
	$0C00-$0fff = we use this as TEXT/GR offscreen buffer
	$1000-$1fff = 4k free
	$2000-$3fFF = HGR1 page	; note we never use HGR2 ($4000-$6000)
	$4000-$9600 = roughly 20k(?)
	$9600-$BFFF = DOS3.3
	$C000-$FFFF = peripherals/ROM