Feature markers

I wanted to wait for some PR being passed to ship it with tests, nevermind ...
Hope the markers are self explanatory.
Here's a screenshot of a random city.
![capture decran 2014-02-17 a 16 07 34](https://f.cloud.github.com/assets/721659/2186427/6120cbd2-97e5-11e3-82b9-5de740a475de.png)