input: Write a python function to create a generator that yields Fibonacci numbers up to a given limit.
  assert list(fibonacci_generator(10)) == [0, 1, 1, 2, 3, 5, 8]
  assert list(fibonacci_generator(1)) == [0, 1]
  assert list(fibonacci_generator(0)) == [0]
output: def fibonacci_generator(limit):
      a, b = 0, 1
      while a <= limit:
          yield a
          a, b = b, a + b