adding support for audiovault.net

[brightening-eyes]

Checklist

• [ x] I'm reporting a new site support request
• I've verified that I'm running youtube-dl version 2020.05.08
• I've checked that all provided URLs are alive and playable in a browser
• I've checked that none of provided URLs violate any copyrights
• I've searched the bugtracker for similar site support requests including closed ones

Example URLs

• Single movie: http://audiovault.net/downnload/10963

Description

this website is a donation based website which describes movies for blind and visually impaired people.
it requires account creation, which can be created on the website. other users can upload audio described videos (they require granting access).
all the files are in audio-only format like mp3 or ogg
thanks