Integrate the C++ implementations of the divergence operator into the working branch features/CPP_Parity_Ops

[Tony-Drummond]

Is your feature request related to a problem? Please describe.
Incremental work bring MOLE's C++ implementations to parity with MATLAB/Octave implementations.

Describe the solution you'd like
Merge the new C++ implementations of the divergence operator from features/CPP_Parity_Ops_New to features/CPP_Parity_Ops for reviews of this work.

Additional context
This issue is a part of Issue #303 and the Draft PR #315