code: func StemTokens(tokens []string) []string {
  	eng := porter2.Stemmer
  	stems := []string{}
  	for _, w := range tokens {
  		if len(w) == 1 {
  			switch w {
  			case "'", "\"", ",", ".", ":", ";", "!", "?":
  				continue
  			}
  		}
  		w = strings.ToLower(w)
  		stems = append(stems, eng.Stem(w))
  	}
  	return stems
  }
docs: // StemTokens returns the porter2 (snowball) stems for each token passed into
  // it.