Added Chlorine to allowed atoms for Cantherm.
Fixed transcription error for Sulfur experimental enthalpy of formation at 0K.

Now matches http://www.gaussian.com/g_whitepap/thermo.htm
Cantherm: added energy corrections for Chlorine for CBS-QB3 methods.
Added BAC for H-Cl bond for CBS-QB3 method.
Adding Chlorine to the allowed atomtypes for RMG-Py.

Can now add species including chlorine to your input files either
using smiles or adjacency lists.  RMG families currently cannot handle
chlorine, but they can be added as either inerts or reactive species
if a reaction library is given.