The 2024 Reboot

This is a complete rewrite, keeping things that worked and discarding
some stuff that needs another place to exist.

What is gone:

  - The idea of literate markdowns as a low level testing tool. Testing
    markdowns using themselves only brough pain. We'll have a more
    traditional testrunner now, still producing TAP.
  - All of the code. We'll keep some ideas, but this is being drastically
    simplified.
  - MIT licensing. Old code within the branch is still licensed with that
    one though.

What remains:

  - We try not to negotiate portability. That is our goal, we do this
    so you don't have to.
  - We will try to provide first-class tools for working with shell
    scripting.