code: func Open(filename string, mode os.FileMode, options *Options) (*Store, error) {
  	options = fillOptions(options)
  
  	encode = options.Encoder
  	decode = options.Decoder
  
  	db, err := bolt.Open(filename, mode, options.Options)
  	if err != nil {
  		return nil, err
  	}
  
  	return &Store{
  		db: db,
  	}, nil
  }
docs: // Open opens or creates a bolthold file.