C++ Named Module Port

[mccakit]

I ported to here, and made the tests pass, I would like it to live in a seperate branch here
https://github.com/mccakit/subprocess/tree/main

[benman64]

Please explain what you want me to do. What do you think if I made it into a header only library? It's not far from header only if you define SUBPROCESS_AMALGAMATE_SOURCES before including subprocess.hpp it becomes almost what you would expect out of a header only library. I haven't had time to integrate with an amalgamation tool to generate the single header file as one would expect. I haven't used c++ modules so I know little about them, it does appear to me that header only is easier for people to integrate than modules. Do you have opinion on this topic?

[mccakit]

Header only libraries bloat out compile times and pollute the namespace. Incremental builds with modules are much faster.
Headers also cause some bugs, because inlining stuff is weird.