Develop preliminary map editor (Define floors, walls, rooms and
	positions of objects)

	Introduce collisions with walls and corners.
	
	Add early enemy intelligence and test collision routine.
	
	Introduce map control points, modifying level editor.
	
	Use map control points to guide aliens to the player.
	
	Add sound effect routine and develop a triggering routine so events
	can cause noises.
	
	Replace simple directional sound with control-point directional sound
	
	Generalise object drawing routine to handle a database of objects
	which the game logic can manipulate, allowing the introduction of
	new objects (Eg player and enemy bullets).
	
	Introduce 'hot spots' to the map, defining areas which trigger things
	like opening doors, logging on to computer terminals, activate alarms
	and so on.
	
	Modify map editor to include hot spot definition