Added in comments to most files.
	modified:   Book.cpp
	modified:   Book.h
	modified:   CD.cpp
    modified:   CD.h
	modified:   Item.cpp
	modified:   Item.h
	modified:   Magazine.cpp
	modified:   Magazine.h
	modified:   ShoppingCart.cpp
	modified:   ShoppingCart.h
	modified:   main.cpp