GSoC week 2
We want to refactor Machine base class to be stateless, but not all algorithms can be stateless. The non-parametric machine need labels and features to be stored in class. So it is convenient that divide the whole machine family into non-parametric and parmetric. The basis idea is add a new interface called NonParmetric, then change all class (such as knn, gp) that require labels and features become the subclass of NonParmetric. Meanwhile, we also want to only set labels and feature when the train is called.