Added calcs, members, & getters for M, u, G, & F.

The members _molarMass, _intEnergy, _gibbsEnergy, _helmholtzEn, and
_chemPoten were added.  These are the air molar mass, specific internal
energy, specific Gibbs free energy (enthalpy), Helmholtz free energy,
and chemical potential, respectively.  Accessor methods were written for
each new member and their calculations were included in
calculateProperties();