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.
I'm not sure it is worth it to `import scipy.ndimage as sp` for one function call.  The comment can then be cut.  Also, it used to be standard to not abbreviate `scipy` to `sp`.  I searched and couldn't find this recommendation in the numpy/scipy style guide, but I may have missed it.  Either way, in this case, it is misleading as the function is in `scipy.ndimage` not `scipy`.