Show users a static page while the site is rendering

I use rack-jekyll on [Openshift](http://www.openshift.com) and currently when I upload changes to Openshift, it restarts Rack and during the rendering process, Rack responds to any requests with a 503 making people think that the site is down or broken.  This patch shows a simple page to the user during the rendering process to tell them to check back shortly.

The page that is displayed (I called it the "wait page") can be specified by Rack-Jekyll users if they don't like the default one.

I also fixed an issue with "auto".  The Listen object was not being started so it wasn't working.