input: Write a python function to generate and print a multiplication table for a given range.
  assert multiplication_table(1, 3) == '1  2  3  \n2  4  6  \n3  6  9  \n'
  assert multiplication_table(4, 5) == '16  20  \n20  25  \n'
  assert multiplication_table(2, 4) == '4  6  8  \n6  9  12  \n8  12  16  \n'
output: def multiplication_table(start, end):
      result = ''
      for i in range(start, end + 1):
          for j in range(start, end + 1):
              result += str(i * j) + '  '
          result += '\n'
      return result