#2789: added cross-validation and automatic determination of regularization parameter (naive CV is slow!).
Research produced ACM Algorithm 642.f (Fortran) for univariate cubic spline smoothing with generalized cross-validation in O(n) described in HUTCHINSON, M. F., AND DE HOOG, F.R. Smoothing noisy data with spline functions. Numer. Math. 4 7 (1985), 99-106. (TODO: translate to C#)