def find_by_x_and_y(x, y)
      select { |square| square.x == x && square.y == y }.first
    end
def find_by_x_and_y(x, y)
      select { |square| square.x == x && square.y == y }.first
    end
Find the square with the matching x and y co-ordinates

 @param [Fixnum] x
   the x co-ordinate.

 @param [Fixnum] y
   the y co-ordinate.

 @return [Square]
 ==== Example:
   # Find the square at 4,2
   square_set.find_by_x_and_y(4, 2)