Cake first draft

Fleshed out a little bit of the cake function.  Need to do some digitize/bin magic but should work otherwise.  Demo of how to use pyFAI to get bins and other information without re-sampeling the image
Does this data have any meaning for detectors which have not been calibrated or outside of x-ray diffraction?  The issue mentioned only x-ray powder diffraction.  You don't need to run the entire pipeline in `pyFAI` you just need to generate the object.
Actually, you could just pass the angle and radial arrays into the function, which would allow you to use any `pyFAI` like program you wish.
Also why is this information optional?