verbose = flag.Bool("verbose", false, "verbose")
)

var wg sync.WaitGroup        // outstanding fetches
var urlq = make(chan string) // URLs to crawl

// urlFrag is a URL and its optional #fragment (without the #)
type urlFrag struct {
	url, frag string
}

var (
	mu          sync.Mutex
	crawled     = make(map[string]bool)      // URL without fragment -> true