Update 1 (Castling)

This release implements Castling, and Checkmating (as the latter was not explicit before). "Quitting" has been changed to "resigning," and captured pieces -- as well as the total points of material for each player -- are kept track of at the top and bottom of the screen.

Known bug:
When king is in check and bishop rook or queen are more than one space away from resolving it they are unable to do so. This is because of how highlighting is handled, and will be fixed in future versions of the code.