A complete gutting of the internals of ytdl-sub to support functions in our variable syntax, in addition to being able to access a yt-dlp entry's .info.json fields using functions. Functionally, ytdl-sub should still look and behave the same from a user-perspective.
With so many lines of code changed (+8927, -2708), no doubt there will be new issues. Please make a GH issue or reach out on Discord if your config/subscriptions break in any way/shape/form.
Details on how to use function support will come soon in the form of proper documentation in our readthedocs.
Adds the following prebuilt presets:
```
"Single"
"SoundCloud Discography"
"YouTube Releases"
"YouTube Full Albums"
"Bandcamp"
```
which require no config.yaml to use. Usage examples can be found in the `/examples` directory
Closes GH Issue #766, partially closes#520
Prior to this release, no other subscriptions would download if a subscription before it had an error. Now, subscriptions will continue to download even if one has an error, and will be reported in the output summary.
