Added
- added lasso and ridge as default estimators and gave them default grids for both `Forecaster` and `MVForecaster`
- added `reduce_Xvars()` method to `Forecaster` object
- added `util` module with one function (for now) to plot error changes from calling the `Forecaster.reduce_Xvars()` method
Changed
- Changed default hyperparameter grid values for knn, xgboost, and lightgbm estimators
Fixed