Changed the basic structure of the matrix to nil instead of 0
Change methods of board to work with nil instead of 0
Refactored the get_diagonal method and eliminated the anti_diagonal method
Refactor check_winner_col and row methods
Another refactor to check_diagonal. To check winner and to position available
removed the change_value method
Removed the attributes for Display and change them as method atributes. Clean switch_player name to be snakecase