Added units to wilhoit parameters for monatomic spc

Cantherm was throwing an invalid quantity error for
species like H as the units were not explicitly
mentioned for wilhoit parameters. The units added are
Cp, Cp0 and CpInf (J/(mol*K))
H (J/mol)
S (J/(mol*K))

The output was checked for H atom with primary thermo
library and looks okay.
Merge branch 'master' of github.com:GreenGroup/RMG-Py
Fixing math overflow error for Cv (vibrational)

Sometimes when the frequency is large it results in
exp(Beta*h*freq) to cause a math overflow. For now
one of the fix is to assume Cv = 0 when x > 500.

If exp(x) >> 1 then
Cv += x * x * exp(-x)
For values of x > 500 this should be very small number
and it is safe to assume it is 0.
Merge branch 'master' of github.com:GreenGroup/RMG-Py
Attempt to overcome case sensitivities for bath gas collider efficiencies.

Retain case when loading kinetics libraries.