handled special case in anova_f_test, CHAID notebook added

- handled a special case in anova f test which was causing error in boston housing dataset
- CHAID section added in notebook

[View](https://gist.github.com/mazumdarparijat/985a516614cb358b8fb7)
Aren't you using 20 bins below? :-) You can maybe just remove (10), it is understandable from the order of the arguments, IMO.