Add random movement for both players

Added random movement for both White and Black players. For White, this
is for debugging purposes only. White's random movement functionality
can be enabled or disabled with the global variable debugWhiteRandom.

Added updating of each player's list of pieces after each move.

Stubbed out the Player base class because we may not need it.

Added several comments to improve program readability.

Updated the README accordingly.
Merge pull request #4 from bmitzel/add_random_movement

Add random movement for both players