Set possible rules at specific position.
        :param x: X coordinate.
        :param y: Y coordinate.
        :param rules: Value to set.

def put(self, x, y, rules):
        # type: (int, int, List[PlaceItem]) -> None
        """
        Set possible rules at specific position.
        :param x: X coordinate.
        :param y: Y coordinate.
        :param rules: Value to set.
        """
        self._field[y][x] = rules