MEMO is a card memory game, so the aim is to find all the pairs of cards that
have been laid face down randomly on the game board.
By means of a frame-shaped pointer that moves in 8 directions (up, down, left,
right and the diagonals), the player selects the cards. When a card is
uncovered, the player must locate its twin: in case of failure, the card is
hidden again; otherwise the pair is removed from the board.
When all the pairs are found, the player goes to the next round.