Make the SSDP registry minimally useful.

cmd/example_ssdp_registry/example_ssdp_registry.go

@@ -0,0 +1,27 @@
+package main
+
+import (
+	"log"
+
+	"github.com/huin/goupnp/ssdp"
+)
+
+func main() {
+	c := make(chan ssdp.Update)
+	srv, reg := ssdp.NewServerAndRegistry()
+	reg.AddListener(c)
+	go listener(c)
+	if err := srv.ListenAndServe(); err != nil {
+		log.Print("ListenAndServe failed: ", err)
+	}
+}
+
+func listener(c <-chan ssdp.Update) {
+	for u := range c {
+		if u.Entry != nil {
+			log.Printf("Event: %v USN: %s Entry: %#v", u.EventType, u.USN, *u.Entry)
+		} else {
+			log.Printf("Event: %v USN: %s Entry: <nil>", u.EventType, u.USN)
+		}
+	}
+}