echos 1.0.3

New features

• Added reservoir scaling parameter tau to train_esn(), enabling dynamic control of reservoir size.
• Added tune_esn() to tune hyperparameters alpha, rho and tau via time series cross-validation (i.e., rolling forecasts).
• Added S3 methods summary.tune_esn() and plot.tune_esn() to summarize and visualize results from hyperparameter tuning.

Bug fixes

• Fixed train_esn() so n_initial is only auto-set when NULL.

Improvements

• Added input validation for y and inf_crit in train_esn() and levels in forecast_esn().
• Improved documentation