Symmetry handling.

[phockett]

Now mostly in place, using libmsym base routines and trimmings.

• Main docs: working with symmetry .
• Commits 18th - 20th April 2023 (cfd7b40 and few preceding) for main changes.

Todo:

• Mapping to ePS term symbols, see previous work in ePSman for this.
  • Aug 2024 update: see CO2 work (theory_symmetry_140723_CO2-Dinfh-ePScompUpdate.ipynb ) for updated ePS comparisons and tests. Still needs some work on m/mu mapping.
• Verification of m and mu mappings, inc. degeneracies and phases. May still have issues here, should check phase terms and also dipole mapping (

  PEMtk/pemtk/sym/_dipoleTerms.py

  Line 72 in d498762

  def dipoleTermsSymHarm(self, reCartMap = {-1:'y',0:'z',1:'x'}, dimMap = {'C':'Cont', 'mu':'it'}):

  ) is complete. (See also SymHarm bug #8.)
• Application of ang mom coupling limits, could apply these to m <> mu mappings.