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

stanza/component_test.go

@@ -67,7 +67,7 @@ func TestParsingDelegationIQ(t *testing.T) {
 				return
 			}
 			if forwardedIQ.Payload != nil {
-				if pubsub, ok := forwardedIQ.Payload.(*PubSub); ok {
+				if pubsub, ok := forwardedIQ.Payload.(*PubSubGeneric); ok {
 					node = pubsub.Publish.Node
 				}
 			}