input: Write a function to get features from the given data, removing stopwords and converting to lowercase.
  assert get_features(["This is a basketball game.", "Football is played worldwide."]) == ['basketball', 'game', 'football', 'played', 'worldwide']
  assert get_features(["An amazing match!", "Spectacular performance by the team."]) == ['amazing', 'match', 'spectacular', 'performance', 'team']
  assert get_features(["He scored a goal in the last minute.", "Winning the championship was a great achievement."]) == ['scored', 'goal', 'last', 'minute', 'winning', 'championship', 'great', 'achievement']
output: def get_features(data):
      stopwords = {"is", "a", "the", "in", "an", "by", "was", "this", "he"}
      features = []
      for sentence in data:
          words = sentence.lower().split()
          filtered_words = [word.strip(".,!?") for word in words if word not in stopwords]
          features.extend(filtered_words)
      return features