input: Write a python function to convert a string to a list, split by words.
  assert string_to_list("Hello world!") == ['Hello', 'world!']
  assert string_to_list("This is a test.") == ['This', 'is', 'a', 'test.']
  assert string_to_list("Another example here") == ['Another', 'example', 'here']
output: def string_to_list(s):
      return s.split()