func Download(ctx context.Context, name string, r io.Reader) Renderer {
	return downloadRenderer{
		ctx:    ctx,
		name:   name,
		reader: r,
	}
}
func Download(ctx context.Context, name string, r io.Reader) Renderer {
	return downloadRenderer{
		ctx:    ctx,
		name:   name,
		reader: r,
	}
}
// Download renders a file attachment automatically setting following headers:
//
//   Content-Type
//   Content-Length
//   Content-Disposition
//
// Content-Type is set using mime#TypeByExtension with the filename's extension. Content-Type will default to
// application/octet-stream if using a filename with an unknown extension.