Ffmpeg-normalize

* Fix unit tests.

* Improve handling of output file folder and errors.

* Clarify usage of output options, add warning.

* Improve documentation, fixes 120.

* Do not include bump messages in changelog.

* Use measured offset in second pass, fixes 119.

* Update release instructions.

* Remove author names from changelog.

* Update release script and changelog template.

* Apply pre-filters in all first passes, fixes 118.

This allows properly reading the level for any kind of normalization, even if
filters affect the loudness in the first pass.

* Add all commits to changelog.

* Remove python 2 support.

* Add quiet option, fixes 116.

- Add a new quiet option
- Promote some warnings to actual errors that need to be shown
- Add a very basic test case

* Improve release script.

* Python 3.8.

* Only print length warning for non-EBU type normalization.