code: func (d *Document) Keywords() map[string]int {
  	scores := map[string]int{}
  	for word, freq := range d.WordFrequency {
  		normalized := strings.ToLower(word)
  		if util.StringInSlice(normalized, stopWords) {
  			continue
  		}
  		if _, found := scores[normalized]; found {
  			scores[normalized] += freq
  		} else {
  			scores[normalized] = freq
  		}
  	}
  	return scores
  }
docs: // Keywords returns a Document's words in the form
  //
  //    map[word]count
  //
  // omitting stop words and normalizing case.