Fix #5 and improve with dropdown

![screenshot from 2014-07-31 22 20 30](https://cloud.githubusercontent.com/assets/2338778/3773905/74efe4ce-191b-11e4-93aa-7f5b59e11a5c.png)
![screenshot from 2014-07-31 22 20 21](https://cloud.githubusercontent.com/assets/2338778/3773906/7508bb8e-191b-11e4-9eb4-8db27f41a7ec.png)

I think if you put a `<ul>` inside a `<li>` in the `nav` element, is to do a dropdown so I set it as default.
It can be an alternative of jQuery dropdown, what do you think @keenanpayne ?