code: func doImage(w http.ResponseWriter, kind string) {
  	img, err := assets.Asset("image." + kind)
  	if err != nil {
  		http.Error(w, "Not Found", http.StatusNotFound)
  	}
  	contentType := "image/" + kind
  	if kind == "svg" {
  		contentType = "image/svg+xml"
  	}
  	writeResponse(w, http.StatusOK, contentType, img)
  }
docs: // doImage responds with a specific kind of image, if there is an image asset
  // of the given kind.