Baptiste Pesquet

Hi, first of all I think you did a awesome job with this project. I use it as a blueprint for mine. As the title says, I wonder why you...

- [ ] Add definition of learning

- [ ] Better ROC/AUROC explanation (https://stats.stackexchange.com/questions/132777/what-does-auc-stand-for-and-what-is-it, https://stats.stackexchange.com/questions/180638/how-to-derive-the-probabilistic-interpretation-of-the-auc)

- [ ] Math output problem with Rise - [ ] Plotly in Colab - [ ] Improve polynomial and regularization code

- [ ] Gradient math proof ([source](http://www.oranlooney.com/post/ml-from-scratch-part-2-logistic-regression/)) - [x] Colors in multiclass decision boundaries

- [x] Hide useless cells - [x] Boosting - [ ] Add voting example - [ ] Move ensemble chapter to a dedicated notebook ?