Handle already archived videos.

Fix error when fetching an unavailable subtitles list.

Fix concurrency issues by adding a new argument for maximum number of concurrency, default is 16.

YouTube-MA is fully working!
Now generating a proper JSON file like YTDL do, with various subs, streams and any other interesting informations in there!

Fix a lot of bugs, I've tested it on big list of IDs etc to detect common bugs.
Unavailable videos crash fixed, same for age restricted that is now bypassed.

I changed "fetching" with "downloading" in the subtitle download log. That deserve a proper release.

Better logging.

Process API-less archiving from single ID or list of IDs, with concurrency using goroutines.
Download annotations, thumbnail, informations, description, and subtitles when available.