Ffmpeg-normalize

* Print warning for bit depths > 16, addresses 163.

* Re-raise error on ffmpeg command failure.

This prevents incorrectly telling the user that a normalized file was written when it wasn't.

* Set tqdm lock for logging only when multiprocessing is available.

Multiprocessing is not available in all environments, for example
on AWS lambda python run time lacks /dev/shm, so trying to acquire
a multiprocessing Lock throws an OSError. The module could also be
missing in some cases (ex. Jython, although this library doesn't support
Jython anyway).

The solution to this is to only try to set the lock when multiprocessing
is available. The tqdm library solves this in the same manner.

For more details: https://github.com/slhck/ffmpeg-normalize/issues/156

* Add instructions on how to run tests.

* Bump requirements, should fix 155.

* Move all examples to Wiki.

* Update badge link.

* Add python_requires to setup.py.

* Improve README.

* Add GitHub actions badge.

* Add GitHub actions tests.

* Properly convert EBU JSON values to float.

* Switch to f strings, remove Python 3.5 support.

* Format code with black.

* Fix flake8 errors.

* Factor out method.

* WIP: new tests.

* Log to stderr by default to enable JSON parsing.

* Remove release script.