Support for PEP 794

[henryiii]

PEP 794 support needs to be added. I think we could normalize the requirement (part before the ;private, and normalize the spacing around ;private - maybe requirement ; private? Or requirement; private? The former matches the PEP, and the later looks more like the format for requirement markers.

Also, where should it be placed in the ordering?

[gaborbernat]

requirement; private

Would be my vote.

Also, where should it be placed in the ordering?

I'd put it right after package name and version.