Initial commit
Add all sliding piece, most of stepping piece
Add Knight
Add color property and Pawn
Create new file 'piece.rb' and 'board.rb' for Board class
Change color to symbol
Set pawns on new board
Set all pieces on board
Create [] method in board, modify piece to use it
Made pos accessible
Make Board#find_king
Added Board#in_check?, #opposite_color, and #all_pieces
Add Board#[]= , #move
Added Board#dup to deep duplicate
Improves Board#dup, adds Piece#move_into_check?
Adds Board#move\!, new #move
Corrects Board#dup
Fixed Board#dup, Piece#move_into_check?
Clean up code
Added Board#checkmate? and fixed Pawn#moves