Standardize macro names as part of next major release

I am proposing that we standardize macro names as part of the next major release.

Specifically: should everything be PUMI_ or SCOREC_ (in this case, the actual pumi library could still have PUMI_).

e.g. PUMI_HAS_ZOLTAN, PUMI_PYTHON_INTERFACE, SCOREC_USE_CGNS, SCOREC_NO_MPI, SCOREC_CXX_WARNINGS all seem inconsistent.

Personally I do not have a strong preference but I would like more consistency. Once a decision is made, we should update STYLE.md.

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