Added toCantera() methods to NASAModel and NASAPolynomial.
Added toCantera() methods to NASAModel and NASAPolynomial.

Not adding them to other thermo classes because Cantera can only handle
NASA polynomials at this time.

Obviously using them requires Cantera (and its Python interface).

KEHANG/RMG-Py,comocheng/RMG-Py,nyee/RMG-Py,enochd/RMG-Py,pierrelb/RMG-Py,chatelak/RMG-Py,enochd/RMG-Py,pierrelb/RMG-Py,faribas/RMG-Py,nickvandewiele/RMG-Py,chatelak/RMG-Py,nyee/RMG-Py,jwallen/ChemPy,nickvandewiele/RMG-Py,comocheng/RMG-Py,faribas/RMG-Py,KEHANG/RMG-Py