Ffmpeg-normalize

* Add pre-and post-filter hooks, fixes 67.

This allows users to specify filters to be run before or after the actual
normalization call, using regular ffmpeg syntax.
Only applies to audio.

* Document audiostream class.

* Warn when file is too short, fixes 87.

* Update release method to twine.

* Handle progress output from ffmpeg, fixes 10.

* Merge pull request 99 from Nottt/patch-1.

fix -cn description

* Fix -cn description.

* Add nicer headers for options in README.

* Add version file in release script before committing.

* Add option to keep original audio, fixes 83.

* Add pypi badge.

* Allow release script to add changelog for future version; upload to pypi.

* Add release script.

* Add small developer guide on releasing.

* Move HISTORY.md to CHANGELOG.md.

* Fix ffmpeg static build download location.

* Bump version.

* Cap measured input loudness, fixes 92.

* Bump version.

* Fix handling of errors with tqdm.

* Improve readme.

* Delete issue template.

* Bump version.

* Clarify extra argument options, move to main entry point.

* Update issue templates.