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 :-) Actually if  I start the loop from i=1, I need to put an if block around it for the case when ```num_vecs==1``` (we would have to skip this code segment in which case). 
Using my strategy, we no longer need the extra if block. If you feel that this looks to much 'hack-y' I can change it right away?