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
But there is no reason that we have to use the `pyFAI` version of encoding this.  I would much rather encode this information as a set of (optional) parameters.  The problem with taking `pyFAI` objects as input is that this function then becomes useless if our data is not XPD data we have run the entire pipeline in `pyFAI`.