two-third spline

[sklesse]

Hi Andy et al.

In my recent paper (https://www.sciencedirect.com/science/article/pii/S1125786520301259) I take issue with the application of the two-third spline and that I do not think it is a good default setting within dplR.

I would suggest setting the default spline to a sort of high-pass filter preset of ~30 years, as this kind of application is the most widely used. nyrs could still be set to "-n", where n is the n% spline as specified in ARSTAN. In addition, I could envision an implementation of a dataset-wide MSL-based two-third spline nyrs="MSL" as another variant to include.

Cheers, Stefan