Add make_kings to Board, can now find and king pieces
Refactor Board functions to raise errors, update switch_player function in Checkers.
Refactor to properly raise RuntimeError exceptions and allow game to continue
Fix typo in Board, add play command to Checkers to run from terminal (not in irb).
Add color to piece symbols, Modify Board display, minor refactor in Checkers play loop. (I'm avoiding the real work to allow multiple jumps...)