added binary denoising notebook

http://nbviewer.ipython.org/gist/Jiaolong/c971175818df85f2c181
In fact, since we use fixed size of images, we can define full-connected factor graph model and use different parameters for different pairwise factors, but it will make the computation very slow.

I have tried it for 10x10 images, and it works very well but for images larger than 20x20, it is extremely slow.