Fixing up the interface.
	new file:   arraylist.cpp
	new file:   arraylist.h
	new file:   singlylist.cpp
	new file:   singlylist.h
	new file:   doublylist.cpp
	new file:   doublylist.h
	modified:   arraylist.cpp
	modified:   arraylist.h
	modified:   singlylist.cpp
	modified:   singlylist.h