(pre-publish) PEP 771: Default Extras for Python Software Packages

[jamestwebber (James Webber)]

@pf_moore

One thing does bother me in particular - why did you need to modify importlib.metadata? Because if that was necessary, this may need to be a core Python PEP rather than just a packaging standard - which is very unusual.

It looks like the only real difference is the addition of the Default-Extra key.