* [infoq] Add audio only format if available
Refactor cookie code into a function.
Renamed formats to http_video, http_audio, rtmp_video
Renamed extract functions to video instead of videos as they return
one or no video.
* [infoq] Rename to _extract_cookies as it more than one
* [infoq] Remove redundant determine_ext
* [infoq] Add comment about hardcoded URL
* [infoq] Use _hidden_inputs instead of messy regex
* [infoq] Probe if audio URL is valid
Make it possible to pass headers to _is_valid_url
* [infoq] Add audio only test
· Import from compat what comes from compat. Yes, some names are available in utils too, but that's an implementation detail.
· Use _match_id consistently whenever possible
· Fix some outdated tests
· Use consistent valid URL (always match the whole protocol, no ^ at start required)
· Use modern test definitions
