Forecast evaluation

Toolset forecast_evaluation: 2 tools.

Tool	What it does	Notes
`forecast_evaluate`	Scores model forecasts against actuals with any of 25 metrics: point (MAE, MSE, RMSE, MAPE, sMAPE, WAPE, ND, bias, cumulative error, relative MAE), scaled by the seasonal naive (MASE, MSSE, RMSSE, scaled PIS), quantile (pinball, multi-quantile, scaled CRPS) and interval (coverage, Winkler, calibration).
`forecast_rectify`	Learns how each model’s backtest error (actual minus forecast) depends on the step ahead and on chosen features, with a correction regressor per step (or one using the step as a feature), and adds the predicted error to new forecasts.

Inputs, limits and outputs are described in Fincept Forecast. Full schemas: fincept_describe_tool.