Handle --get-url with merged formats (fixes #2883)

Outputs one URL per line
[tvigle] Update test and modernize
[bliptv] Add support for audio-only files (Fixes #4404)
Merge branch 'master' of github.com:rg3/youtube-dl
Merge pull request #4395 from cryptonaut/issue2883

Handle --get-url with merged formats (fixes #2883)