Ffmpeg-normalize

* Add way to force dynamic mode, clarify usage, fixes 176.

* Add warning for cover art, addresses 174 and 175.

* Update README.

* Improve issue templates.

* Do not print ffmpeg progress in debug logs.

* Remove unused import.

* Replace which() function with shlex version.

* Add python 3.10 in setup.py.

* Clarify minimum ffmpeg version.

* Properly detect -inf dB input.

* Debug command output for ffmpeg commands.

* Remove unneeded warning message.

* Use astats instead of volumedetect filter, fixes 163.

Allows floating point calculation.