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)


1: This method has to return a value, otherwise `scipy` complains because it cannot put a value in the output of `generic_filter`
2: If we make it a method of the class the first variable passed to it would have to be the graph(self), but `scipy` will pass the array of values first.