DOC : stub for wedge integration (caking)

Work for #17
There may be statistical uncertainty issues with re-sampling the image see [Simon's paper on 2D detector uncertainty](http://arxiv.org/abs/1309.3614).  This is much more simply handled by just using pyFAI to handle the binning of the raw (potentially tilted) image directly into q/tth.  Additionally pyFAI will produce an array of theta angles (which go from 0 to 360 around the ring).