input: Write a python function to find the sum of all numbers in a given range.
  assert sum_of_range(10, 20) == 165
  assert sum_of_range(1, 5) == 15
  assert sum_of_range(0, 0) == 0
  assert sum_of_range(-5, 5) == 0
output: def sum_of_range(start, end):
      return sum(range(start, end + 1))