input: Write a python function to split a string by a given delimiter.
  assert split_string('Hello,World', ',') == ['Hello', 'World']
  assert split_string('apple|banana|cherry', '|') == ['apple', 'banana', 'cherry']
  assert split_string('one-two-three', '-') == ['one', 'two', 'three']
output: def split_string(s, delimiter):
      return s.split(delimiter)