so that the effect of the term on the enthalpy equation is optional

At the specie level:
    hs = sensible enthalpy
    ha = absolute (what was total) enthalpy
    es = sensibly internal energy
    ea = absolute (what was total) internal energy

At top-level
    Rename total enthalpy h -> ha
    Rename sensible enthalpy hs -> h

Combined h, hs, e and es thermo packages into a single structure.

Thermo packages now provide "he" function which may return either enthalpy or
internal energy, sensible or absolute according to the run-time selected form

alphaEff now returns the effective diffusivity for the particular energy which
the thermodynamics package is selected to solve for.