code: def pad(self, pad):
          
          tile = self.copy()
          tile.l -= pad
          tile.r += pad
          return tile
docs: Pad this tile by an equal amount on each side as specified by pad
  
          >>> Tile(10).pad(2)
          Tile [-2, -2, -2] -> [12, 12, 12] ([14, 14, 14])
  
          >>> Tile(10).pad([1,2,3])
          Tile [-1, -2, -3] -> [11, 12, 13] ([12, 14, 16])