Adds support for natural coordinate system
Adds multiple move execution
Adds Piece#valid_move_seq?
Adds HumanPlayer and basic game loop.
Fixes Board#dup, apparently causing the game loop to function correctly.
Fixes another bug with dup that was preventing kings from working.
Adds colored highlighting to last move.
Refactors so translate_loc lives in the player class, instead of being an orphan.
Also moves the board and piece classes to separate files.
removes calls to translate_loc from board and piece methods.
Refactors the way that the move methods in Piece raise errors to be less dumb.