Remove superfluous property
Add API revision constant
Argument to getAncestors|Descendants is deprecated
Add method getDescendantsAndSelf()
Add getAncestorsAndSelf() method
Verify that nodes don’t use own ID as parent ID

This throws an exception which would not have been
thrown before if this is the case. Hence, it might
break backward compatibility, but only if the data
data is inconsistent.
Fix incorrect doc comment
Add example for get(), add info on 1.1
Add PHP versions 5.5 and 5.6
Add tests for the new methods