[PATH] Add ability to register new users with the jabber server

[mtodd]

Originally submitted by saimonmoore with a path included; please refer to http://code.google.com/p/xmpp4r-simple/issues/detail?id=6#makechanges

Simple usage:

im = Jabber::Simple.register(jid, passwd)

• will try and register user on the server
• if successfull, will reconnect and send default status presence
• if not successfull, throws a RegistrationError with a detailed message

  self.register method signature:

self.register(jid, password, status = nil, status_message = "Available") #So you can still provide custom status after registration