input: Write a function to find the maximum absolute difference between any two elements in an array.
  assert max_difference([7, 1, 3, 8, 25]) == 24
  assert max_difference([1, 1, 1, 1]) == 0
  assert max_difference([-10, 5, 3, -2, 0]) == 15
output: def max_difference(arr):
      return max(arr) - min(arr)