Change the way Wilhoit class stores/calculates E0
Change the way Wilhoit class stores/calculates E0

The constant of integration H0 is not equal to the enthlapy at 0K,
so the parameter E0 has to be calculated instead of just returning H0.
faribas/RMG-Py,KEHANG/RMG-Py,pierrelb/RMG-Py,enochd/RMG-Py,chatelak/RMG-Py,comocheng/RMG-Py,nyee/RMG-Py,pierrelb/RMG-Py,nyee/RMG-Py,KEHANG/RMG-Py,chatelak/RMG-Py,comocheng/RMG-Py,nickvandewiele/RMG-Py,nickvandewiele/RMG-Py,enochd/RMG-Py,faribas/RMG-Py