pyproject.toml: include subpackages in setuptools config

[ichard26]

The glob patterns (include/exclude) must match the entire package name to take effect, so we need to add a wildcard pattern for subpackages. Otherwise, any wheels built won't include subpackages (like pathspec.patterns) and things will break >.<

To see the impact of the invalid configuration simply try the following:

• pip install https://github.com/cpburnz/python-path-specification/archive/master.zip (pip will build a wheel from source and then install it)
• python -c "import pathspec"
• See it blow up with ImportError: cannot import name 'patterns' from partially initialized module 'pathspec'

Thank you for maintaining pathspec by the way! 🖤 I am one of the maintainers of Black which uses pathspec and it's been great. I noticed this issue since I run black's test suite daily using the development versions of our dependencies (to catch issues early-on, before they get released).

[cpburnz]

Thanks for finding this. It's odd that pip lets this pass when building the wheel from the source distribution but not a ZIP.