Refactored and implementing an interface.
Another implementation of World using a PackedLong
Updated RefactorLife to test TestPackedWorld.  Also forgot that the
packed long is not passed by reference...
Now supports both TestArrayWorld and TestPackedWorld via a command line
switch.
Abstracting base class for common functionality
Removing direct field access to width and height in the two Test...World
classes.  Implementing ArrayWorld inheriting from WorldImpl,
functionally identical to TestArrayWorld
Updating comments
Implementing a world with a PackedLong, this time extending WorldImpl.
Fixing PackedWorld constructor to be zero parameters; using subclasses
of WorldImpl in RefactorLife
Using WorldViewer to render the world as it evolves.
Importing and implementing sample code for AgingWorld.