v1.4.2: more bugfixes and merged SPLS and PLS

v1.4.0: Made many changes aimed at fixing bugs (particularly a few that occurred when using MLPs, RNNs, or LCEN with lag > 0) or increasing the number of hyperparameters the user can directly pass to main_SPA(). Another important housekeeping change includes finally calling LCEN (and its hyperparameters or subvariables) as LCEN.
Gradient-Boosted Decision Trees and AdaBoost models were also added, and all tree-based and SVM models were parallelized.
Finally, more examples were added, and the old MATLAB files/code were removed.

v1.4.2: fixed some bugs, including one that appeared when using LCEN with lag > 0 and LCEN_transform_y == True. Merged SPLS and PLS, since PLS is just a special case of SPLS with eta = 0; also parallelized SPLS. Made the input variable scaling more robust and made it obey what the user requested via function inputs.