input: Write a python function to compute the Manhattan distance between two points.
  assert short_path((1, 2), (5, 6)) == 6
  assert short_path((0, 0), (3, 4)) == 7
  assert short_path((2, 3), (2, 3)) == 0
output: def short_path(p1, p2):
      return abs(p1[0] - p2[0]) + abs(p1[1] - p2[1])