Session is implemented - update README
A few improvements in PLAIN auth

* make callback method name more meaningful
* use Close() call to close a stream
Roster implementation
Add <presence> stanza implementation
Implement XEP-0115: capsnode
Factory.AddConstructor: get namespace from XMLName
Add XEP and RFC fetcher
Merge pull request #10 from dotdoom/master-features

Added presence, presence/c. Some Improvement to auth logic. Elements registration re-factoring.