Light-of-day SciTokens C++ Release!

v0.1.0 celebrates the very first version of the SciTokens C++ library worth seeing the light of day.

It features most of the same concepts as the Python library - the SciToken, the Validator, and the Enforcer. This should be worth a look from anyone previously embedding the Python library into a C or C++ application (the library actually exports a C-linkage API, even though the implementation is in C++).

As it's not a "1.0" release, don't be awfully surprised to find things like memory leaks, bugs, or crashes. Bug reports are always appreciated -- and pull requests even more!