input: Write a python function to perform sentiment analysis on a given tweet and return the sentiment score.
  assert sentiment_analysis('I love programming in Python!') in ['P+', 'P', 'NEU', 'N', 'N+', 'NONE']
  assert sentiment_analysis('This is the worst day ever.') in ['P+', 'P', 'NEU', 'N', 'N+', 'NONE']
  assert sentiment_analysis('I am feeling okay today.') in ['P+', 'P', 'NEU', 'N', 'N+', 'NONE']
output: def sentiment_analysis(tweet):
      from vaderSentiment.vaderSentiment import SentimentIntensityAnalyzer
  
      analyzer = SentimentIntensityAnalyzer()
      sentiment_dict = analyzer.polarity_scores(tweet)
  
      if sentiment_dict['compound'] >= 0.05:
          return 'P' if sentiment_dict['compound'] < 0.5 else 'P+'
      elif sentiment_dict['compound'] <= -0.05:
          return 'N' if sentiment_dict['compound'] > -0.5 else 'N+'
      else:
          return 'NEU'