input: Write a python function to capitalize the first letter of each word in a sentence.
  assert format_sentence("He went to the store") == "He Went To The Store"
  assert format_sentence("this is a test sentence") == "This Is A Test Sentence"
  assert format_sentence("PYTHON programming LANGUAGE") == "Python Programming Language"
output: def format_sentence(sentence):
      return ' '.join(word.capitalize() for word in sentence.split())