changes.002

乒乓球游戏程序

* Added the `objects' module to coordinate the game objects.
* Added the `bat' module to handle a bat.
* Added a `global' module, to define global variables, such 
	as screen dimensions, bat settings, etc.
* Extended the `input' module to get left/right input, to 
	move the bat.
* Made the `display' module call the `objects' module to draw
	the objects, using a subbitmap of the screen.