Attach footer to bottom

Hi, I really like the new gatling.io website but I feel that the footer should always be at the bottom of the page. 

It is not at the bottom when browsing pages without enough content (and therefore height) on large screens. For example, see the following pages: http://gatling.io/docs/ and http://gatling.io/services/.

I modified the CSS so that instead of this:
![gatling io-1](https://cloud.githubusercontent.com/assets/7253680/4027487/81b62a5c-2c2f-11e4-96ab-78ff474f8764.png)

we get this:
![gatling io-2](https://cloud.githubusercontent.com/assets/7253680/4027489/8983a656-2c2f-11e4-9159-f294f7733c48.png)