Versioning: switch to ~ and ^ for pre- and post-release versions
    
    This makes versioning vastly simpler from the packager POV:
    - the upstream release can *always* be manipulated into Version that sorts
      properly.
    - downstream information is contained solely in the Release field, and
      it can be bumped without any drama.
    
    This is based on other drafts, in particular
    - https://pagure.io/packaging-committee/pull-request/908.
    
    Also see:
    - https://fedoraproject.org/wiki/PackagingDrafts/TildeVersioning
    - https://github.com/rpm-software-management/rpm/pull/597
    
    The guidelines go into quite a lot of complexity to cover complicated
    cases. But nowadays 99% of upstreams use fairly mundane release
    numbering schemes, so almost all packaging scenarios will be covered
    by simple uses of plain numbers, with an overwhelming majority of the
    remaining sliver covered by an occasional insertion of ~pre or ^post.