Turning Surface into SPA: dev repo with demo

Just to share experience.

Here is the source code and working demo: https://github.com/englishextra/serguei-surface-dev

### The goal

Turn Surface docs into SPA.

### Fixes

 - Load page content via AJAX
 - Make Nav close on click on nav links and on content window as well
 - reassign events on elements upon new content loaded via AJAX
 - Minor fixes in HTML markup