Aiaprep completed

Proper (hopefully) testing for the aiaprep() function that's been in development for quite some time, and for the associated affine transform.

While mostly finished, this still needs a few things to be done to it (ie: @Cadair still wants a few things done to it):
* [x] Modify Map.rotate() to use image.rotate(), then change aiaprep() to call Map.rotate()
* [x] Remove the C code for the Crotate function and delete relevant bits from setup.py
* [x] Normalisation of images for the skimage warp() function may not be general enough to always work - there's probably a much cleverer way of doing it.
* [x] Improve docstrings
* [x] make sure docs are being built
* [ ] add more tests, and make them pass travis.
Is there a good reason to have this large test?  If one of the pieces fails it is going to be hard to know which part.  Also, please introduce some newlines for readability, and perhaps some comments explaining what is being tested for.