Force File Name

[smhmd]

Referencing: davidde/mpv-autosub#8, davidde/mpv-autosub@bdc5a6c

The ability to force a file name regardless of the input.

$ subliminal download -l en 'gibberish.file.name.for.a.movie.mkv'
# fails
$ subliminal download -l en 'my movie (date)' -o 'gibberish.file.name.for.a.movie.mkv'
# successes

This will mitigate an edge case when streaming a file with a filename that isn't helpful to subliminal. the proper file name can be fed to subliminal by the script/user.