echos 1.0.4

Improvements

• Expanded package documentation, vignettes and README to better describe the ESN architecture, key hyperparameters, model selection procedure and tuning workflow.
• Clarified the role of the formula argument in ESN() for the fabletools model interface.

Datasets

• Renamed m4_data to m4_monthly_subset to clarify that the dataset contains a monthly subset of the M4 competition data. The old name m4_data is retained for backward compatibility.
• Improved documentation for m4_monthly_subset and synthetic_data.