input: Write a python function to compare two strings and return a match score using difflib.
  assert compare_strings("Hello", "hello")==1.0
  assert compare_strings("Python", "python")==1.0
  assert compare_strings("Python", "Java")==0.0
output: def compare_strings(str1, str2):
      import difflib
      return difflib.SequenceMatcher(None, str1.lower(), str2.lower()).ratio()