Spline smoothness constraint only implemented for degree=3 #5
Description
For consistency, it may be beneficial to implement bsmooth=TRUE for a general polynomial degree. Currently only cubics (degree 3) are allowed. Any degree is allowed with bsmooth=FALSE, which draws directly on the splines2 basis.
On the other hand, will anyone ever need degrees other than 3? Discussion welcome. Principle of the package is to have a single default model that works well generally.