code: func FileHandler(path string, fmtr Format) (Handler, error) {
  	f, err := os.OpenFile(path, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0644)
  	if err != nil {
  		return nil, err
  	}
  	return closingHandler{f, StreamHandler(f, fmtr)}, nil
  }
docs: // FileHandler returns a handler which writes log records to the give file
  // using the given format. If the path
  // already exists, FileHandler will append to the given file. If it does not,
  // FileHandler will create the file with mode 0644.