For the Tests/ folder, the next time we add a new type of files, we simply need to add a new glob pattern.
The source distribution is now in sync with the content of the repository as returned by `git ls-files`
it's better to group man pages in a separate sub-folder in case we add alternative doc formats in the future, or if we add additional man pages.
This also allows to read man pages directly from the source tree, e.g. via `export MANPATH=Doc/man`, or `man -M Doc/man ttx`
We need this as we no longer use setuptools_scm to retrieve the full list of files under version control.
Instead, we need to spell them out one by one.
Hopefully we don't forget anyone...
One notable absence was README.md... :)
For the testdata/*, I now use `include_package_data=True` in setup.py, to automatically install any data files found inside package directories that are also specified in MANIFEST.in file.
I also include the Snippets, which I think should belong to the source distribution, despite not being installed as console scripts like ttx, etc.
The MANIFEST.in does not need to include itself (done by default).
