[compoundmedia] Add new extractor

[kevgrig]

Before submitting a pull request make sure you have:

• At least skimmed through adding new extractor tutorial and youtube-dl coding conventions sections
• Searched the bugtracker for similar pull requests
• Checked the code with flake8

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• I am the original author of this code and I am willing to release it under Unlicense
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What is the purpose of your pull request?

• Bug fix
• Improvement
• New extractor
• New feature

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Description of your pull request and other information

New extractor for https://www.compoundmedia.com/. No tests because all videos require authentication.

[kevgrig]

@dstftw Hi, I believe all the requested changes are resolved and the Travis build passed. Can you please re-review?

[dstftw]

You must provide account credentials for any further work on this.

[kevgrig]

@dstftw I wasn't aware of that requirement. I don't like the security and privacy implications of that. Thanks for your consideration.

For any others interested, I simply patched my distribution-installed package:

$ echo "from .compoundmedia import CompoundMediaIE" | sudo tee -a /usr/lib/python3.7/site-packages/youtube_dl/extractor/extractors.py
$ sudo curl -o /usr/lib/python3.7/site-packages/youtube_dl/extractor/compoundmedia.py https://raw.githubusercontent.com/ytdl-org/youtube-dl/1f27d68da21a251b0c57e5e6dbba04a2f68414d2/youtube_dl/extractor/compoundmedia.py
$ cat >> ~/.netrc
machine compoundmedia login $EMAIL password $PASSWORD
Ctrl^D
$ youtube-dl -n https://www.compoundmedia.com/shows/...
[...]
[CompoundMedia] Logging in
[CompoundMedia] Requesting Metadata
[livestream] [...]: Downloading JSON metadata
[livestream] [...]: Downloading SMIL file
[livestream] [...]: Downloading m3u8 information
[livestream] [...]: Downloading f4m manifest
[hlsnative] Downloading m3u8 manifest
[hlsnative] Total fragments: [...]
[download] Destination: [...].mp4
[download] 100% of [...]MiB in 01:35
[ffmpeg] Fixing malformed AAC bitstream in "[...].mp4"