Mandelbox in more than 3 dimensions

[quick-dudley]

I suppose "Feature Requests" is the best place to put this, but rather than a request I've got a patch that you can decide whether or not to incorporate. I hope it's self-explanatory because I haven't written any comments.
The filename I had used for the attachment is mandelbox9d.patch but patch is not one of the allowed file suffixes.

What it does:
The basic mathematical description of the mandelbox is independent of the number of dimensions. This patch effectively adds 6 optional extra vector components which allows the user to view different 3D slices of a 9D mandelbox.