Add responsive menu

Hi guys i did make a menu mobile like Zeno's blog (#112), i hope you enjoy. 

![screenshot_2014-07-08-07-06-11](https://cloud.githubusercontent.com/assets/2338778/3508364/502667d8-068a-11e4-8f4c-e6e96cc97212.png)
![screenshot_2014-07-08-07-06-03](https://cloud.githubusercontent.com/assets/2338778/3508365/502ad35e-068a-11e4-86b9-e6f88434f897.png)

.desktop-only {