Initialized Checkers Branch
Added Piece#initialize and Piece#move_offsets
Implemented empty board initialization and display
Implemented board setup with pieces and full board display
Implemented sliding moves, fixed bug in Piece#move_offsets
Implemented jumping (capturing) moves
Refactored Piece@symbol => Piece#symbol, Piece#move_offsets now uses #direction
Implemented basic Checkers game class
Added HumanPlayer class with move input parsing
Implemented basic game loop
Implemented basic game play with two human players.  Can move and capture.  No multi-captures
Implemented multi-jump captures
Implemented game state save/load, conceding, and exiting
Removed debugging statement
Merge branch 'checkers'