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)


Try to avoid while loops when a for loop will work. I think this should work:

```python
for position in np.nditer(arr, flags=['multi_index']):
```

This removes the need for a separate initialisation line (105 above) and increment line (120 below).