adds match_to and first_rel_to

This just gives you two easy ways of matching to a specific object.

`match_to` is just shorthand that adds `self.where(neo_id: node.neo_id)` for you, nothing revolutionary but saves you some repetitive code. It returns a QueryProxy object so you can build on it easily.

`first_rel_to` returns the first relationship to a given node over a QueryProxy chain. Nil if none.

I find myself doing this stuff manually all the time and when writing up some docs for my talk next week, thought it might be nice to add methods that make it a little easier.