Lots of miscellaneous API cleanup and streamlining, including...
- Modified StateMachine so that States no longer need to be explicitly
added.
- Changed StateMachine to no longer maintain a Set of States that have
been added.
- After realizing that a State's identifier is no longer used in any
meaningful way, it was removed from State. However, since it came in
handy for debugging, I kept it in DefaultState but renamed it to
description.
- EqualityUtil was removed because its only method was fairly trivial
and was only used in one place.