Fixes #72. Update URL, introduce error when ListenAndServe fail.

1. The URL where the server is running is updated so that it can be
clicked from the terminal, in case the terminal supports it.
2. The error is thrown if the port cannot be bound by the tutorial
server.

Author: Anubhav Saini

main.go

@@ -382,14 +382,19 @@ func handle(root string) func(w http.ResponseWriter, req *http.Request) {
 }
 
 var (
-	host = flag.String("host", "localhost:8000", "Serving host")
+	protocol = "http"
+	address  = "localhost:8000"
+	host     = flag.String("host", address, "Serving host")
 )
 
 func main() {
 	flag.Parse()
-	fmt.Println("Serving Go+ tutorial at", *host)
+	fmt.Printf("Serving Go+ tutorial at %s://%s\n", protocol, *host)
 	http.HandleFunc("/", handle("."))
-	http.ListenAndServe(*host, nil)
+	err := http.ListenAndServe(*host, nil)
+	if err != nil {
+		log.Fatalf("Failed to start server at %s://%s.\nError: %s.", protocol, *host, err)
+	}
 }
 
 // -----------------------------------------------------------------------------