Have link to

`have_link_to` allows for matching a particular URL regardless of the link text. This makes it easier to change link text during development so long as the behavior remains the same. 

Example (rails, rspec):

    page.should have_link_to new_post_url

I have less understanding of the code under `node`, which I believe is used outside of rspec. There was little documentation that I could find about adding to it, so my changes right now lie only under the `rspec` directory, but I'd be happy to change that with a little advice.