Documenting each cmod_x.cpp with description of purpose

[dguittet]

Is your feature request related to a problem? Please describe.
Within each cmod_x.cpp compute_module, the inputs and outputs are described in the var_info table. While the descriptions are minimal, they offer info for HOW to use the module. However, the purpose of the compute_module itself is not documented in the file, and makes it difficult to figure out WHAT it is used for.

Describe the solution you'd like
A clear and descriptive comment above the var_info table documenting the module's purpose.

Currently, the description is a brief statement at the bottom of the page, ie:

DEFINE_MODULE_ENTRY( 6parsolve, "Solver for CEC/6 parameter PV module coefficients", 1 )