Report internal variables

[JohnRuhl]

After the calculations are done, we often need to access variables that are currently calculated (or could be calculated) "on the fly" and then discarded. These include:

Psat
Flink
G
P_electrical
V_bias
dP/dI (for converting NEP <-> NEI)
dP/dT_cmb
dP/dT_rj

(I'm using this "issue" as a place to keep this list and hopefully keep track of which ones are still "to do")