Added callback to process errors after connection.

Added tests and refactored a bit.

_examples/xmpp_component/xmpp_component.go

@@ -35,7 +35,7 @@ func main() {
 		IQNamespaces("jabber:iq:version").
 		HandlerFunc(handleVersion)
 
-	component, err := xmpp.NewComponent(opts, router)
+	component, err := xmpp.NewComponent(opts, router, handleError)
 	if err != nil {
 		log.Fatalf("%+v", err)
 	}
@@ -47,6 +47,10 @@ func main() {
 	log.Fatal(cm.Run())
 }
 
+func handleError(err error) {
+	fmt.Println(err.Error())
+}
+
 func handleMessage(_ xmpp.Sender, p stanza.Packet) {
 	msg, ok := p.(stanza.Message)
 	if !ok {