Inconsistency in dimensionality in heat flux evaluation within slab model is rectified.

[joshi994]

TYPE: Bug fix

KEYWORDS: Slab model, sensible heat flux, heat capacity. skin temperature, thermal balance

SOURCE: Parag Joshi (Brookhaven National Laboratory)

DESCRIPTION OF CHANGES:
Problem: The sensible heat flux evaluation in the slab model is incorrect. The flux is missing the factor of thermal capacity.

Solution: The error is fixed following the formulation and verified by evaluating the dimensions post corrections.

ISSUE: For use when this PR closes an issue.
Fixes #123

LIST OF MODIFIED FILES: list of changed files (use git diff --name-status master to get formatted list)

TESTS CONDUCTED:

1. No test is performed for quantifying the impact of the error.

RELEASE NOTE: The sensible heat flux evaluation turned out to be dimensionally inconsistent which led to the incorrect evaluation of the ground temperature. Following the formulation (Link: https://journals.ametsoc.org/view/journals/apme/21/11/1520-0450_1982_021_1594_ahrmot_2_0_co_2.xml), refer to the equations 5a and 11 of the article in the link, the error is highlighted.

[dudhia]

The units of FLHC are W/m2/K, so this code is already correct.