Change supersaturation definition

[trontrytel]

I would like to change our supersaturation definition. What we currently have is: S = q_vap / q_sat - 1

S is typically defined as a ratio of partial pressures p_vap / p_vap_sat - 1. The outcome will be close, but not exactly the same.

It should not affect the Thermodynamics package because we don't use S to compute anything internally. But I would like to use it in CloudMicrophysics in some of the ice nucleation parameterizations

cc: @tapios, @amylu00, @szy21

[szy21]

Sounds good, I didn't know these two are different...

[tapios]

Sounds good to me.