CubicSpline: For Csat of any phase

The cubic spline fit is implemented as described in:

William H. Press, Brian P. Flannery, Saul A. Teukolsky, William T. Vetterling, Numerical Recipes in C: The Art of Scientific Computing, Cambridge University Press, 1992.

The columns T (temperature), C(heat capacity), and d2C/dT2 (i.e., the second derivative with temperature) correspond to arrays xa, ya, and y2a in the implementation of spline in section 3.3 of the reference (page 116).

The heat capacities are assumed to follow a simple T cubed form below the lowest temperature reported. The original

Evaluation Results: