Add the regularization calibration

It would be nice to implement the regularisation calibration proposed by de Lavenne et al. (2019) (https://doi.org/10.1029/2018WR024266). That would stabilise parameters for downstream basins.

Basically, we need to consider in the calibration process the distance between calibrated parameter values and parameter values of upstream catchments.

That would be useful for @cyril.thebault as well as Laura and other people using airGR-SD.

I would say that we need for that:

• to have access to upstream parameter values in Calibration_Michel

• add a regul boolean in CreateCalibOptions and retrieve it in Calibration_Michel

• either a new Error_Crit that allows to combine any Error_Crit with the distance calculation, or implement directly that in Calibration_Michel

• distance must be calculated in the transformed space of parameters to avoid having parameters with huge distance (e.g. X1) compared to smaller parameters (e.g. X4)

• certainly other things that will come up when we try to implement it. :)

Who wants to give it a try? :)