Adds classes for all pieces and their move array
Adds Board class; adds #moves to all Piece subclasses
Adds Pawn#moves
Fixes SteppingPiece#moves bug
Fixes bug in Pawn#moves. Creates Board#setup_board, Board#dup, Piece#dup, Board#in_check?.
Adds Board#display
Adds game and HumanPlayer classes, fixes bugs in Board#dup and typo in Pawn#captures. Makes it pretty.
Reorders Piece subclass methods for clarity, makes some private. Makes some changes to Pawn#moves, #captures, #moves_to_empty and SlidingPiece#moves for clarity & brevity.
Adds message for winner on checkmate; adds error handling for incorrect move input.
Adds error handling, Check notification, and a jail to display captured pieces.
Adds alternative Board#display method
Adds castling.
Adds pawn promotion. Fixes bug with printing jail in second Board#display method.