Add fast frugal trees

[BTopcuoglu]

• Create new models to be used
• Test with real data

[JMAStough]

I'd like to help with this if it's cool with yall

[kelly-sovacool]

I'd like to help with this if it's cool with yall

@JMAStough Awesome! Sorry we didn't notice your comment until just now. I believe these would be custom models to implement, see caret docs here: https://topepo.github.io/caret/using-your-own-model-in-train.html.
Maybe @BTopcuoglu knows more about the details.

Let us know if you have any questions about the newly refactored code base.

[kelly-sovacool]

Note: @zenalapp is working on L1 logit for #154

[kelly-sovacool]

L1 logistic regression is now supported since we switched to glmnet (#154). We should probably document which custom hyperparameters the user needs to provide to pick L1 vs L2.

[zenalapp]

Yes I think that should be in the hyperparameter tuning vignette.