Revisit the Python guidelines
    
     - drop references to EOL Fedoras
     - introduce %python3, %python2 (and mention %python)
     - introduce %pycached
     - introduce %python3_platform
     - drop _python_bytecompile_extra - we will work to deprecate it
    
    Full %pycached specification is hidden in
    https://src.fedoraproject.org/rpms/python-rpm-macros/c/6c63a5b7f484f3c4b6bee13196561c9b1dff410a
    But I deemed it too overwhelming to be put into the guidelines.