download.go
func ToWriter(src string, w io.Writer, options Options) error {
	u, err := url.Parse(src)
	if err != nil {
		return errors.Wrap(err, "invalid src URL")
	}
	return FromURL(u, w, options)
}
func ToWriter(src string, w io.Writer, options Options) error {
	u, err := url.Parse(src)
	if err != nil {
		return errors.Wrap(err, "invalid src URL")
	}
	return FromURL(u, w, options)
}
// ToWriter downloads the specified `src` URL to `w` writer using
// the specified `Options`.