func UniqueURLsMapFromFlag(fs *flag.FlagSet, urlsFlagName string) map[string]struct{} {
	return (*fs.Lookup(urlsFlagName).Value.(*UniqueURLs)).Values
}
func UniqueURLsMapFromFlag(fs *flag.FlagSet, urlsFlagName string) map[string]struct{} {
	return (*fs.Lookup(urlsFlagName).Value.(*UniqueURLs)).Values
}
// UniqueURLsMapFromFlag returns a map from url strings got from the flag.