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)


I agree that an example would help, perhaps under an "examples" section? @vighneshbirodkar you could create a minimal RAG, define a "weight update function", and do a couple of merges, showing the result.