code: func (fkvs *FileKeyValueStore) Store(key interface{}, value interface{}) error {
  	if key == nil {
  		return errors.New("key is nil")
  	}
  	if value == nil {
  		return errors.New("value is nil")
  	}
  	file, err := fkvs.keySerializer(key)
  	if err != nil {
  		return err
  	}
  	valueBytes, err := fkvs.marshaller(value)
  	if err != nil {
  		return err
  	}
  	err = os.MkdirAll(filepath.Dir(file), newDirMode)
  	if err != nil {
  		return err
  	}
  	return ioutil.WriteFile(file, valueBytes, newFileMode)
  }
docs: // Store sets the value for the key.