Region Adjacency Graph

## Example Images
![figure_1](https://cloud.githubusercontent.com/assets/3823490/3291718/5ce9b952-f587-11e3-8c29-e2aace6d7794.png)
![figure_2](https://cloud.githubusercontent.com/assets/3823490/3291723/7074b134-f587-11e3-8c73-d28222891a21.png)


@vighneshbirodkar You may well be right about speed, though in my experience I'd often happily sacrifice a few ms to have a single, unified algorithm. It really helps for maintainability. Though I'll echo @jni in wishing for full N-d in an ideal world.