HTMLFormatter

Added a simple HTMLFormatter that outputs the RuboCop offenses to a html file.
If i change the indentation the `pre` tag gets all ugly.
And the output would be 
![1](https://cloud.githubusercontent.com/assets/3598553/4046474/9ea12974-2d32-11e4-80a2-96bc9340aaa4.png)

and not 

![2](https://cloud.githubusercontent.com/assets/3598553/4046480/a4e42890-2d32-11e4-8ae1-e642bfe4e74d.png)