add railroad-classic example


I was wondering how to represent a railroad in the style that was used pretty often in the 20th century, for examples 
The Flushing line shown in this picture...
![rr-example](http://25.media.tumblr.com/6448de9915d434c8e13fca99d301ad3f/tumblr_mpysqqeRPb1syx7edo1_1280.jpg)


After some searching, I couldn't find any examples of how to do it, so I figured it out myself and thought to share it. 

Here's an example of it in use. 

![hdm-example_rr](https://f.cloud.github.com/assets/955351/1133988/2a36fb60-1be8-11e3-8f49-5eafbe07bf18.png