[xpra-codecs-freeworld/f30] (6 commits) ...Release 3.0

Summary of changes: 935cfae... rebuilt (*) 24987a3... Release to 2.5.3| Switch to Python3 definitively (*) d339219... Fix Changelog (*) 6960425... Rebuild for new ffmpeg version (*) 36a7d44... Rebuild for python-3.8 (*) c665010... Release 3.0 (*) (*) This commit already existed in another branch; no separate mail sent