Cplus ize printf

[fromage17]

Martin, this PR (cplus-ize-printf) has been updated and now supersedes the other PR (fix-clang-tidy-notifs).
It contains:
a) it contains consts/constexprs for all magic #s, and provides the formulas that underlie computation of the exponent;
b) it addresses all your feedback from PR fix-clang-tidy-notifs;
c) it contains various bug fixes to floating point representations, especially %g use cases;
d) it eliminates an infinite-recursion risk that had been present;
e) it passes all Test Cases, clang-tidy, and cppcheck -- and I added many floating-point Test Cases;
f) it contains the RespiraWorks pre-commit checks;

With your permission, I'll close the old PR (fix-clang-tidy-notifs). This current PR supersedes it.

Here's what's next, as I see it:

1. Upon your approval, I'll squash commits and rebase to the HEAD of master (the rebase will be a trivial operation as master hasn't changed in awhile);
2. As you specified, I'll put printf and its README into its own dir next to nanopb;
3. I'll make it compatible with c++17, and make it more c++-style;
4. I'll do some needed cleanup of the code, test cases, and README;

Looking forward to your feedback!

[fromage17]

Martin,
I've updated this PR's branch again --- the Makefile now builds only what's needed, instead of "everything". Added targets for running clang-tidy, cppcheck, and the test_suite itself.
I will update this branch again with more improvements. Next: C++17 compatibility.
==Scott