Log Message:
youtube-dl 2017.07.15

Core
[YoutubeDL] Don't expand environment variables in meta fields

Extractors
[spiegeltv] Delegate extraction to nexx extractor
[nexx] Add support for nexx.cloud
[generic] Fix rutube embeds extraction
[karrierevideos] Fix title extraction
[youtube] Don't capture YouTube Red ad for creator meta field
[slideshare] Fix extraction
[5tv] Add another video URL pattern
[drtv] Make HLS and HDS extraction non fatal
[ted] Fix subtitles extraction
[vine] Make sure the title won't be empty
[twitter] Support HLS streams in vmap URLs
[periscope] Support pscp.tv URLs in embedded frames
[twitter] Extract mp4 urls via mobile API
[niconico] Fix authentication error handling
[giantbomb] Extract m3u8 formats
[vlive:playlist] Add support for playlists