Log Message:
youtube-dl: Update net/youtube-dl to 20180721

Changes:
2018.07.21
----------
Core
+ [utils] Introduce url_or_none
* [utils] Allow JSONP without function name (#17028)
+ [extractor/common] Extract DASH and MSS formats from SMIL manifests

Extractors
+ [bbc] Add support for BBC Radio Play pages (#17022)
* [iwara] Fix download URLs (#17026)
* [vrtnu] Relax title extraction and extract JSON-LD (#17018)
+ [viu] Pass Referer and Origin headers and area id (#16992)
+ [vimeo] Add another config regular expression (#17013)
+ [facebook] Extract view count (#16942)
* [dailymotion] Improve description extraction (#16984)
* [slutload] Fix and improve extraction (#17001)
* [mediaset] Fix extraction (#16977)
+ [theplatform] Add support for theplatform TLD customization (#16977)
* [imgur] Relax URL regular expression (#16987)
* [pornhub] Improve extraction and extract all formats (#12166, #15891, #16262,
  #16959)