cleaning and refactoring
Player#parse_user_input replaces validate_user_input and accepts multiple move
refactoring
all logic for a turn now in take_turn
Adds @pieces and #dup to Board class
Board#dup duplicates each piece
starts implementing Piece#perform_moves and Piece#valid_moves_seq?
move_sequence now doesn't include original position
Piece#performs_moves now works
refactoring
multiple move works
adds win logic which doesn't work and ugly testing method