Abstract Factory pattern

	Pizza Store example in abstract-factory.vsd

	Example: Java's ability to run GUIs in different UI styles
	How could you design a system so that the UI style can be switched
		without modifying the application's source code?
	
	Generic diagram in abstract-factory.vsd

	Another Example: Different levels of difficulty in a computer game
		abstract factory creates different kinds of characters, 
			objects, obstacles
		BeginnerFactory, IntermediateFactory, ExpertFactory