code: func (model *Model) SaveLight(filename string) error {
  	model.Lock()
  	for term, count := range model.Data {
  		if count.Corpus < model.Threshold {
  			delete(model.Data, term)
  		}
  	}
  	model.Unlock()
  	return model.Save(filename)
  }
docs: // Save a spelling model to disk, but discard all
  // entries less than the threshold number of occurences
  // Much smaller and all that is used when generated
  // as a once off, but not useful for incremental usage