code: func readFilesInDir(dir string, out map[string]string) error {
  	_, err := os.Stat(dir)
  	if os.IsNotExist(err) {
  		return nil
  	}
  	return filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
  		if err != nil || info.IsDir() {
  			return err
  		}
  		body, err := ioutil.ReadFile(path)
  		if err == nil {
  			out[path] = string(body)
  		}
  		return err
  	})
  }
docs: // readFilesInDir loads content of files into a map "file path" => content.
  //
  // Used only for small HTML templates, and thus it's fine to load them
  // in memory.
  //
  // Does nothing is 'dir' is missing.