code: func (tz *TzArchive) DeleteIndex(idx int) error {
  	if idx >= tz.NumFiles {
  		return errors.New("index out of range of number of files")
  	}
  
  	tz.files = append(tz.files[:idx], tz.files[idx+1:]...)
  	return nil
  }
docs: // DeleteIndex deletes an entry in the archive by its index.