[core] Decode environment variables with filesystem encoding (Fixes #3854, Fixes #3217, Fixes #2918)

Introduces compat versions of os.getenv and os.path.expanduser
[utils] Add posix expanduser implementation and clarify the original source
[ard] Add rss support
Added extractor for crunchyroll 'playlists' i.e. series. so that one can, e.g. download all episodes of a series
Forgot to reverse extracted video urls so they are in correct order for video selection args
[ard] make rss match more universal
Initial version of audiomack.py
Added init.py initializer
Finished audiomack extractor
Made changes per phihag
Not directly calling soundcloud extractor anymore
Credit @winwon for vidzi (#3989)
Merge remote-tracking branch 'xavierbeynon/audiomack'
[nhl] Improve video URL extraction (Closes #4013)
[audiomack] Simplify
Apply --keep-video to --recode-video originals
Merge branch 'master' of github.com:rg3/youtube-dl
[lrt] Updated test
[soundcloud] Modernize and fix tests
[tumblr] Fix extraction (fixes #4029)