Processing many images at once

Would be really cool to be able to run a repa parallel array on a large chunk of images at once.

Maybe adding a z component to a new version of makeImage and an (Int -> FilePath) to a new version writeImage?

[lehins]

You can technically do that already by storing many VU images in a one dimensional repa boxed array.

I'll keep this ticket around because ability to represent a sequence of images in a single 3D array has some other perks. This will be possible at some point in the future when I get around to implementing this ticket #30