Update for latest clojuredocs.org site structure

Can you double-check that I'm not misunderstanding something here? I'm pretty confident with the Jsoup change in `clojuredocs_docset/core.clj`, but not entirely confident about the `:httrack` value change in `config.clj`.

In any event, this does seem to generate a working docset for the `clojure.core` namespace, but that doesn't mean it's "right".