Further clean up all code, use the exception mechanism across the board, and make error codes only used internally, when asserting a problem, and not externally represented.

Calling the operating system's API makes a lot more sense.
Exceptions are definitely thrown for non-existent files.
Formatting the source code makes it more readable.
Remove the direct use of the c++ 2011 type trait, All switched to c++2020 concepts and type constraints.
Update README.md

Author: Twilight-Dream-Of-Magic