Add support for a subtitles argument in video URLs

[veganstraightedge]

Currently

[[ https://vime.com/:video_id: ]]

results in

• ✅ an embedded video HTML snippet
• ✅/❌ with English as the default subtitles track

✅ if the video viewed by English speakers only
❌ if the ideo viewed by non-English speakers

Wanted

[[ https://vime.com/:video_id: subtitles:it ]]
[[ https://vime.com/:video_id: subtitles:IT ]]
[[ https://vime.com/:video_id: subtitles:It ]]
[[ https://vime.com/:video_id: subtitles:iT ]]

results in

• ✅ an embedded video HTML snippet
• ✅ with Italian as the default subtitles track

Ignore subtitles arg for non-video URLs