input: Write a python function to generate a random number within a given range.
  assert 5 <= random_number(5, 10) <= 10
  assert 1 <= random_number(1, 100) <= 100
  assert -10 <= random_number(-10, 10) <= 10
output: import random
  
  def random_number(start, end):
      return random.randint(start, end)