Add a new Hydrator for working with DOMNodes

I developed this new hydrator as part of client project and found it to be immensely useful. Its purpose is to extract and hydrate DOMNode instances based on supplied XPath queries.

At this point, I'm submitting this PR as mostly a request for comments on the code. I believe it could be a valuable addition to ZF2, but it might not be exactly in line with the standard way of doing things.