Update lcms2 to 4da8703.
Update .gitignore.
Update unrar to v5.1.4.

5.1.4.tar.gz - 5.10.3 in the rc file...
ISR/VSFilter: Support loading external PGS subtitles.

This commit fixes #1411.
GFN.cpp/.h: Rename the files to SubtitleHelpers.cpp/.h and cosmetics.

Add a new namespace, remove the external array, ...
Factorize the code used to guess the subtitle name and use it for external PGS subtitles.
Docs: Change the tag numbering of LAV Filters/ffmpeg.

Follow the same principle as the nightly builds numbering now that we use `git describe`.

MPC-HC 1.7.5 was a hotfix release so neither LAV Filters or ffmpeg were updated so we won't have any tag collision.
Update ZenLib to v0.4.29 r458.
**Compilation fails** Update MediaInfoLib to v0.7.69.

Need to fix the compilation error upstream first.
Remove trailing spaces.