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
I guess another option is to pass in all the `pyFAI` parameters (point of beam incidence, rotation angles 1,2, and 3, etc.) and generate the arrays on the spot.