Able to specify dirs that will trigger browser refresh

The auto-refresh? feature is great. When playing around with clojurescript, it's nice to be able to control which directories trigger auto refresh. For example, it can be annoying when the browser refreshes when saving cljs files under src/cljs because it will clear any work in a browser repl session.

So, here's a small addition to allow specifying :refresh-path. 

Dave