SpecialFunctions: increase iteration limit of BetaRegularized from 100 to 120
Interpolation: more reasonable LinearSpline implementation
Interpolation: Differentiate2 instead of DifferentiateAll; definite integral; cleanup
Interpolation: add QuadraticSpline (without solver yet)
Interpolation: CubicSpline class (intended to replace old model)
Interpolation: migrate akima and hermite cubic spline to CubicSpline class
Interpolation: migrate cubic spline to CubicSpline class
Drop old redundant spline interpolation classes
Interpolation: use more common terms in Interpolate facade