code: func New() *Corpus {
  	c := &Corpus{
  		words:       make([]string, 0),
  		frequencies: make([]int, 0),
  		ids:         make(map[string]int),
  	}
  
  	// add some default words
  	c.Add("") // aka NULL - when there are no words
  	c.Add("-UNKNOWN-")
  	c.Add("-ROOT-")
  	c.maxWordLength = 0 // specials don't have lengths
  
  	return c
  }
docs: // New creates a new *Corpus