title: finder.apply_ngram_filter in nltk.collocations to classify some ngrams
body: <p>How to use finder.apply_ngram_filter in nltk.collocations to rank only certain ngrams and not the contrary to remove certain ngrams. 
  Is it this: 
  finder.apply_ngram_filter(lambda *w: w not in myngrams)
  or there is another way to do that?</p>
  
  <p>Can someone help?</p>