Add pawn attacking move at its diagonals.

Add an attacking or capturing move for Pawn.
> Unlike other pieces, the pawn does not capture in the same direction that it moves. A pawn captures diagonally forward one square to the left or right (see diagram).
>
> Another unusual rule is the en passant capture. It can occur after a pawn advances two squares using its initial two-step move option, and the square passed over is attacked by an enemy pawn. The enemy pawn is entitled to capture the moved pawn "in passing" – as if it had advanced only one square. The capturing pawn moves to the square over which the moved pawn passed (see diagram), and the moved pawn is removed from the board. The option to capture the moved pawn en passant must be exercised on the move immediately following the double-step pawn advance, or it is lost for the remainder of the game.

For more info, check out the wikipedia entry [here](https://en.wikipedia.org/wiki/Pawn_(chess)#Capturing).

L’issue ne nomme aucun fichier ni test ; commence donc par localiser l’implémentation des déplacements de Java Pawn et les tests existants de génération de coups. Vérifie les captures diagonales ordinaires, puis la règle en passant et son expiration immédiate. Le travail est terminé lorsque les deux comportements de capture sont représentés correctement et que le comportement existant reste intact.

Rédigé par le modèle d'indexation à partir du texte de l'issue.