v1.4.0: tree models, more parallelization, housekeeping

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.