Better handling of optional parameters in a few kinetics models.
Better handling of optional parameters in a few kinetics models.

I had forgotten to set the default Tmin and Tmax of MultiArrhenius to
None. I was also not properly handling the optional T2 parameter in the
Troe falloff expression.

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