Add small extrapolation allowance in ThermoData.
Add small extrapolation allowance in ThermoData.

This is ostensibly so that we can extrapolation from 300 K to 298 K
without needing to give a value for Cp0. A better approach would be to
actually provide the Cp0 (and CpInf), since they are easy to determine
from a chemgraph.

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