Request to add utility files to main repository.

The current version of this fork largely deals with the inclusion of three new classes:
* GameCamera, the start of a possible camera system.
* input.KeyboardHandler, a generic keyboard management class.
* input.MouseHandler, a generic mouse cursor management class.

The two input handler classes currently implement the singleton pattern, or as closely as I can make them in AS3. Most of the logic could be refactored into static methods if desired.