Merge pull request #1 from djwy/master

#place_pieces on Board, add symbols to Piece, and #to_s method for Piece
create #InvalidMoveError, refactor #place_pieces, create #move_piece method
Create Chess class, fix bug in pawn, handle when user tries to move a location that does not have a piece
Fix dup bug, create blank board option, create #in_check_mate method for Board, temporarily change #place_pieces for debugging, create #winnter method
fixed #in_check? infinite call stack, can't move into check, game ends on #in_check_mate
Remove excess methods that are no longer called. Revert #place_pieces.
Move all pieces into folder. Account for trying to #make_move with an empty tile.
Refactor Chess class, HumanPlayer class
Refactor #place_pieces, #make_dirs, #display. Add colors! Minor fixes in Pawn and HumanPlayer.
Add error handling for user input. Add save/load methods but it does not actually do so.
Finalize #save_game and #load_game methods in Chess. Add Chess#switch_turns and code to handle save or load commands.