recognise double-space linebreaks

Two spaces at the end of a line are treated as a <br> line break. It would be nice if a syntax theme were able to recognise and style this. 
![screen shot 2014-12-30 at 13 40 25](https://cloud.githubusercontent.com/assets/2543659/5578527/76bb17e4-9029-11e4-9965-ea7bae55c70d.png)