reduce need to parse subtitles in some codepaths

add title to add-subtitles

add checks to ensure dependency binaries are present on PATH

fixed regression

bump version, remove subs when underflowing due to timing shifts

redid subtitles adding; added add-bulk-subtitles

release: 0.2.4

various improvements

fixed filecheck

notes

Merge pull request #5 from Riizade/bump-0.2.3

bump version

Merge pull request #4 from Riizade/create-output-dir

ensure output dir exists

Update TODO.md