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)


args and kwargs, yes. But "extra_arguments" and "extra_keywords", I have only seen in ndimage.generic_filter so far, with no equivalent form elsewhere. (ie I have not seen "extra_args" used anywhere.)