FoundationNavWalker for WordPress

[Zurb's Foundation](http://foundation.zurb.com) rocks. It's a really simple framework to quickly build sites on, with less basic styling than [Bootstrap](http://getbootstrap.com), and one of my favourite things is the [built in off-canvas menu](http://foundation.zurb.com/docs/components/offcanvas.html).

When trying to build the menu into a WordPress site I was working on recently, I struggled to get it right with wp_nav_menu’s default functionality. After a bit of Googling, and some time in Sublime Text, I built a very basic version of what I needed.

At the moment, it does just about what I need, but I’d love to improve it. I’ve open-sourced the code on GitHub so if you have any improvements, fork it!