c2s.js: make authenticate & register adhere to node conventions
c2s.js: make authenticate & register adhere to node conventions

callbacks have Error as first parameter

opts allow for more flexibility on auth/reg data

eelcocramer/node-xmpp,ggozad/node-xmpp,agebrock/node-xmpp,tempbottle/node-xmpp,node-xmpp/node-xmpp,ggozad/node-xmpp,node-xmpp/node-xmpp,xmppjs/xmpp.js,qbit/node-xmpp,stliu/node-xmpp,agebrock/node-xmpp,xmppjs/xmpp.js,WeBest/node-xmpp,qbit/node-xmpp