PubSub protocol support (#142)

* PubSub protocol support
Added support for :
- XEP-0050   (Command))
- XEP-0060   (PubSub)
- XEP-0004   (Forms)

Fixed the NewClient function by adding parsing of the domain from the JID if no domain is provided in transport config.
Updated xmpp_jukebox example

* Delete useless pubsub errors

* README.md update
Fixed import in echo example

* Typo

* Fixed raw send on client example

* Fixed jukebox example and added a README.md

cmd/fluuxmpp/xmppmuc.go

@@ -7,7 +7,7 @@ import (
 	"gosrc.io/xmpp/stanza"
 )
 
-func joinMUC(c xmpp.Sender, toJID *xmpp.Jid) error {
+func joinMUC(c xmpp.Sender, toJID *stanza.Jid) error {
 	return c.Send(stanza.Presence{Attrs: stanza.Attrs{To: toJID.Full()},
 		Extensions: []stanza.PresExtension{
 			stanza.MucPresence{
@@ -16,7 +16,7 @@ func joinMUC(c xmpp.Sender, toJID *xmpp.Jid) error {
 	})
 }
 
-func leaveMUCs(c xmpp.Sender, mucsToLeave []*xmpp.Jid) {
+func leaveMUCs(c xmpp.Sender, mucsToLeave []*stanza.Jid) {
 	for _, muc := range mucsToLeave {
 		if err := c.Send(stanza.Presence{Attrs: stanza.Attrs{
 			To:   muc.Full(),