input: Write a function to remove all punctuation, special characters, and stopwords from a given tweet. Return the cleaned tweet as a list of words with stopwords removed. 
  assert clean_tweet("I'm so excited to be going to the #MuseumTour! #BigDay #travel")==["excited", "going", "MuseumTour", "BigDay", "travel"]
  assert clean_tweet("This is a test!")==["test"]
  assert clean_tweet("Hello, world!")==["Hello", "world"]
  assert clean_tweet("")==[]
  assert clean_tweet("No stop words here.")==["No", "stop", "words", "here"]
output: def clean_tweet(tweet):
      import string
      from nltk.corpus import stopwords
      stop_words = set(stopwords.words('english'))
      words = tweet.translate(str.maketrans('', '', string.punctuation)).split()
      return [word for word in words if word.lower() not in stop_words]