[Cin] Slight update for differences.pdf

For some reason, today I decided to update the differences.pdf file at: https://cinelerra-gg.org/download/differences.pdf The * in the rightmost column shows lines I changed - not very many, just 25 of them. But the previous last update was 10/25/2019 so I wanted to get it up to date. I did not update the count for formats, codecs, colormodels, decoders, encoders and muxers but will try to do that when FFmpeg 5.1 is released and updated on CinGG.