input: Write a python function to tokenize a given sentence using NLTK and remove punctuation.
  assert tokenize_sentence('Hello, world!') == ['hello', 'world']
  assert tokenize_sentence("What's your name?") == ['whats', 'your', 'name']
  assert tokenize_sentence("Python's great.") == ['pythons', 'great']
output: import nltk
  import string
  
  nltk.download('punkt')
  
  def tokenize_sentence(sentence):
      tokens = nltk.word_tokenize(sentence)
      tokens = [word.lower() for word in tokens if word.isalnum()]
      return tokens