code: func NewNGramIndex(opts ...Option) (*NGramIndex, error) {
  	ngram := new(NGramIndex)
  	for _, opt := range opts {
  		if err := opt(ngram); err != nil {
  			return nil, err
  		}
  	}
  	ngram.init()
  	return ngram, nil
  }
docs: // NewNGramIndex is N-gram index c-tor. In most cases must be used withot parameters.
  // You can pass parameters to c-tor using functions SetPad, SetWarp and SetN.