New release 4.0.0 (modernization release, no functional changes)
    
    This is a new release that I put a lot of work into, but if all
    goes well, package users will notice no difference at all. Behind
    the scenes there's a ton of modernization work both upstream and
    on the package; the package now tries to use all the shiny new
    pyproject-rpm-macros stuff. The spec file is now way simpler and
    will only work on F31+, and I'll only merge it back that far, F30
    and EPEL-7 are now stuck out on branches. Dropping EPEL 7 means
    we can ditch Python 2 builds and conditionalization, and all the
    `python3_pkgversion` and `python3_other` malarkey. Ditching F30
    as well means we can use `pyproject_buildrequires` (though it
    currently doesn't entirely work for us, due to RHBZ #1808601, so
    we still have to list test deps manually, unfortunately).