Ffsubsync

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* Lots of improvements from PRs submitted by alucryd (big thanks!):
* Retain ASS styles;
* Support syncing several subs against the same ref via --overwrite-input flag;
* Add --apply-offset-seconds postprocess option to shift alignment by prespecified amount;
* Filter out metadata in subtitles when extracting speech;
* Add experimental --golden-section-search over framerate ratio (off by default);
* Try to improve sync by inferring framerate ratio based on relative duration of synced vs unsynced;

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* Make default max offset seconds 60 and enforce during alignment as opposed to throwing away alignments with > max_offset_seconds;
* Add experimental section for using golden section search to find framerate ratio;
* Restore ability to read stdin and write stdout after buggy permissions check;
* Exceptions that occur during syncing were mistakenly suppressed; this is now fixed;

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* Use webrtcvad-wheels on Windows to eliminate dependency on compiler;

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* Misc bugfixes and stability improvements;

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* Bugfix for writing subs to stdout;

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* Allow MicroDVD input format;
* Use output extension to determine output format;