Handle filters which unregister themselves in AssExportFilterChain::Clear
Get rid of auto-running exporters, since they aren't really used for anything anymore
Add agi::util::try_parse
Add agi::util::Remove for deleting files
Use CRC32 for ffms2 index filenames

No real advantages other than that it means md5.h/c can be deleted.
Don't write the crash xml file

Nothing uses it and it's not even valid xml.
Cut down on the ifdefs in main.cpp

Shuffle some stuff around to reduces the number of ifdefs and always
define MacOpenFile since there's no reason not to.
Extract options and MRU stuff from main.h

Nearly all of the files including main.h are doing so only for OPT_GET
and friends, which are rather unrelated to the main things that main.h
declares.
Significantly speed up AssDialogue::GetData

wxString::Format is astonishingly slow, and while this normally doesn't
particularly matter, AssEntry::EntryData's speed can become relevant on
large files.

Switch to a slightly more manual approach that's about four times as
fast.
Allow negative values for shadow depth, angle and spacing in the style editor
Write the version comments under the [Script Info] header. Closes #1567.
Drop MPC-HC VSFilter and default to xy-VSFilter