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)


Use for loops, not while:

```python
for i in range l:
```

And while we're at it, it's best not to use variables called `l`, because they are difficult to read. Use `depth`, `width`, `height`.