C4.5 notebook added, C4.5 missing stopping criteria added

- C4.5 notebook added
- stopping criteria added for all same attributes

[Notebook output](http://nbviewer.ipython.org/gist/mazumdarparijat/3e3a812cc3b91b605d66)
@iglesias I thought of that. But again I had to demonstrate the pruning method which wouldn't have been possible if I used the ```CCrossValidation``` class (train and apply happens internally). Maybe in case of CART I can demonstrate the use of ```CCrossValidation``` class.