WIP: Describe array order terminology in 2D, 2D+c, 3D, 3D+c arrays

Still working on it, but just thought I'd check this in so that we can tag it as 0.11.
I can see `l` being used when we have a loop:

```
for l in range(levels):
    for r in range(rows):
        for c in range(cols):
             # do something
```