added binary denoising notebook

http://nbviewer.ipython.org/gist/Jiaolong/c971175818df85f2c181
No, I think we only use theta_p for all pairwise factors in this experiment. Please check cell 11,
`def define_factor_type(num_status, dim_feat)`.

Please also see the text under cell 10:
```
For binary denosing, we define two types of factors:
- unary factor: the unary factor type is used to define unary potentials that captures the the appearance likelyhood of each pixel. We use very simple unary feature in this experiment, the pixel value and a constant value 1. As we use binary label, thus the size of the unary parameter is 4.
- pairwise factor: the pairwise factor type is used to define pairwise potentials between each pair of pixels. There features of the pairwise factors are constant 1 and there are no additional edge features. For the pairwise factors, there are 2×2 parameters.
Putting all parameters together, the global parameter vector w has length 8.
```