Change needed: a solver for a soil moisture reservoir to prevent over-extraction of water by primary fluxes

[RY4GIT]

After discussing with @jmframe and Nels, I figured out it is better to post this as an issue rather than PR.

Please see the PR https://github.com/NOAA-OWP/cfe/pull/66 for the details My debug attempt (Files changed in the PR) is in Python, but hope it is easily translatable to C.