Ffmpeg-quality-metrics

* Fix README.

* Change CLI syntax, add VIF filter.

Move CLI syntax to a more flexible format for selecting metrics.
This is not backwards-compatible, so a major release.
Add the VIF filter.

* Fix bug if VMAF is the only metric.

* Update docs.

* Update docs.

* Deprecate old API.

* Add single calc() function, fixes 32.

* Add dev requirements.

* Explicitly call VMAF model in test.

* Support Python 3.9.

* Fix flake8 errors.

* Simplify VMAF function.

* Detect available filters.

* Note how to update docs.

* Update docs.

* Remove release script.

* Update ffmpeg-progress-yield requirement.

* Format setup.py.

* Add missing CLI option to readme.

* Fix long description content type.