Parse hostnames with constexpr functions into strong types
Ideally invariants in types should afford us to avoid unit testing, by giving us compile (and runtime) guarantee about the contents.
make will run the tests in main.ccp.
Expect the implementation to be buggy.
We rely on the NamedType which is a powerful header only library
included in the repo.
There's also a barebone implementation of gsl::span included.
Apart from std::optional the code should happily compile in C++14
and for now this is a requirement (so no std::string_views alas).