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
Well this goes to my question about what the output should be.  My understanding of how cake works is that it just does standard azimuthal integration only on the portion caked.  In that case you need to know how the mask transformed the data so that an accurate binning can be achieved.