input: Write a python function to find all matches of the word 'the' in a string, ignoring case.
  assert find_matches('The quick brown fox jumps over the lazy dog')==['The', 'the']
  assert find_matches('There are three THEs in this sentence THE THE the')==['THE', 'THE', 'the']
  assert find_matches('No matches here')==[]
output: def find_matches(s):
      import re
      return re.findall(r'\bthe\b', s, re.IGNORECASE)