Additional sub-cooling heat transfer correlations for liquid H2

1. Adding basic thermodynamic functions for rho and Cp at (T,p)
2. Adding heat transfer correlations for boiling film, transient and sub-cooling boiling regimes for liquid-H2.
3. Option to use a correlation-type of HTC for sub-cooling regime instead of the standard RTI model.
4. Minor fix to the thermo for h-Polynomial type.