Missing property: user-select

It seems `user-select` [property](https://developer.mozilla.org/en-US/docs/Web/CSS/user-select) doesn't missed in syntax. And `user-select` support added.

Before
![screen shot 2014-05-13 at 1 20 58 am](https://cloud.githubusercontent.com/assets/67686/2947793/99713e66-d9fa-11e3-9038-8883af6802ac.png)

After
![screen shot 2014-05-13 at 1 23 28 am](https://cloud.githubusercontent.com/assets/67686/2947794/9e307aa2-d9fa-11e3-90e0-32bc12c682f7.png)