SSA subtitles: Fix outline background with \frx or \fry tags.

This commit fixes #2984.
update thirdparty/versions.txt
update Changelog.txt and release date
Update Changelog.txt
bump version to 1.6.7
Updated Greek translation.
MpaDecFilter: missing "return S_OK;"
update Release.txt
update Little CMS to v2.5 (git d504603)
CONTRIBUTING.md: mention the precommit hook script
Readme.md: switch to Atx-style headers
Readme.md: minor improvements
MpaDecFilter: Fix incorrect safety checks.
Updated Catalan translation.

Refs: #2408.