5344421 Automate updating Fedora version in docs

Authored and Committed by Otto Urpelainen 2 years ago
    Automate updating Fedora version in docs
    
    In many places, a Fedora version number is used as and example,
    in strings like Fedora 34, f34, fc34.
    The docs read better if the version is always the current release,
    or perhaps one behind.
    
    AsciiDoc attributes are used to define
    the current and previous OS version
    as well as the current EPEL version
    in one place.
    The attributes are then referred to
    in all examples that need those values.
    
    Resolves #28