input: Write a python function to generate a list of numbers between two given numbers.
  assert numbers_between(1, 5) == [1, 2, 3, 4, 5]
  assert numbers_between(10, 15) == [10, 11, 12, 13, 14, 15]
  assert numbers_between(3, 3) == [3]
output: def numbers_between(start, end):
      return list(range(start, end + 1))