Using the configuration file to define separate configurations

[waahhhh]

Checklist

• I'm reporting a feature request
• I've verified that I'm running youtube-dl version 2019.08.13
• I've searched the bugtracker for similar feature requests including closed ones

Description

It would be pretty nice if we could use the configuration file to define separate configurations.
As example in (TOML-Syntax):

[extractor-a]
x=true
audio-format="mp3"

[extractor-b]
o="S%(season_number)s_E%(episode_number)s_%(title)s.%(ext)s"

If we pass an URL that matches "extractor-a", we get an mp3 file.
If we pass an URL that matches "extractor-b", we get a video file that uses a different output template.