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.
@stefanv @blink1073 I chose `level` because it gives @JDWarner his precious right-handed frame. ;) But I agree that `l` is a crap variable name, and that `depth` has a nice parallel with "Numpy". (NEVER SURRENDER! =P) On the other hand, row and col don't jive with `vstack` and `hstack` anyway... 

The best thesaurus-provided option (imho) is "elevation".