Merge sp into ip - Githubissues

This PR merges NCEPLIBS-sp into NCEPLIBS-ip so that the NCEPLIBS-sp repo can be retired.

Summary:

All of the sp source code is integrated into the ip library, but currently not through a module interface. That way, developers should be able to use it right away without code modification. _In the next release, I'll create an spmod module for consistency with the rest of the library.
Tests all merged. In the next version I'll rebuild the baseline files or tweak the test code so we don't need the big endian flags for the sp tests.
No more sp in the CI (or cmake, of course).
Removed -fimplicit-none for GCC; plan to restore in next version (requires significant code changes).
Disabling bounds checking for a few sp files; plan to do away with this in next version (requires significant code changes).
Updated spack recipe.
Merged and updated documentation.
VERSION -> 5.0.0

Unrelated to the sp merge:

Fixed a bug that was causing issues for building tests with multiple make threads.
Simplified spack CI to reduce number of jobs.
Misc. README/LICENSE updates.

Verification:

Code coverage: The new code is getting checked and everything looks right.
Spack: The updated recipe concretizes, builds, and tests successfully using the latest spack.
Test run time: the develop job takes significantly longer to run, probably because the sp code is no longer being optimized. I'll create an issue for this (either optimize code or split up the work).

Fixes #93 Fixes #209

NOAA-EMC / NCEPLIBS-ip