Implement XPath2

FAQ says concerning XPath 2 that "little interest in this has been shown". I open this issue to give the opportunity to Jaxen users to show that it is not the case (I hope).

Jaxen is the XPath engine used by htmlunit (http://htmlunit.sf.net) and by WebTest (http://webtest.canoo.com) and I think that a lot of users of this 2 open source tools would be interested in XPath 2 support (or at least in some of the new features).

I can imagine that it could be possible to first provide the new XPath functions (for example the regex functions) that don't necessary require changes to the internal data structure. WebTest already provides (in its own namespace) a matches function that should work like the one from the XPath2 spec. This function can be contributed to Jaxen without problem.