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 yes. Actually the iris CSV file contains both string and float in each line. I am not sure if I did it the right way, but I think CSVFile could not handle a mixture of floats with strings.