Adjusted MASE for Hindcast Cross-Validation

[MOshima-PIFSC]

As per Henning's email to Nicholas, a potential update for the adjusted MASE could be implemented that only adjusts the naïve prediction residuals with minimal contrast instead of the MAE (current method). To do this the following changes would be made to SSmase.R (lines 231-234):

scaler <- mean(abs(naive.eval))
scaler <- mean(pmax(abs(naive.eval),MAE.base.adj)
mase <- maepr / scaler
mase.adj <- maepr /scaler.adj

This method would be more targeted at adjusting specific years with very low contrast vs. the entire timeseries.
Additionally, it would be helpful to update the documentation for this function, in the R script and the user handbook to improve understanding of the application and interpretation.

@N-DucharmeBarth-NOAA would you have time and be willing to help us work on this issue to improve the MASE function?

[N-DucharmeBarth-NOAA]

@MOshima-PIFSC let me finish up this blue shark assessment work first and then I can make time to help out with this issue.

[MOshima-PIFSC]

Thanks @N-DucharmeBarth-NOAA no rush!