youtube-dl 2021.05.16

Core

• [options] Fix thumbnail option group name (#29042)
• [YoutubeDL] Improve extract_info doc (#28946)

Extractors

• [playstuff] Add support for play.stuff.co.nz (#28901, #28931)

• [eroprofile] Fix extraction (#23200, #23626, #29008)

• [vivo] Add support for vivo.st (#29009)
• [generic] Add support for og:audio (#28311, #29015)

• [phoenix] Fix extraction (#29057)

• [generic] Add support for sibnet embeds
• [vk] Add support for sibnet embeds (#9500)
• [generic] Add Referer header for direct videojs download URLs (#2879,
  #20217, #29053)

• [orf:radio] Switch download URLs to HTTPS (#29012, #29046)

• [blinkx] Remove extractor (#28941)

• [medaltv] Relax URL regular expression (#28884)

• [funimation] Add support for optional lang code in URLs (#28950)
• [gdcvault] Add support for HTML5 videos

• [dispeak] Improve FLV extraction (#13513, #28970)
• [kaltura] Improve iframe extraction (#28969)
• [kaltura] Make embed code alternatives actually work
• [cda] Improve extraction (#28709, #28937)
• [twitter] Improve formats extraction from vmap URL (#28909)
• [xtube] Fix formats extraction (#28870)
• [svtplay] Improve extraction (#28507, #28876)
• [tv2dk] Fix extraction (#28888)