Pyls-black

* 39 Fixes breaking change introduced in version `21.04b` of `black` (thanks sveitser)
* 33 Release includes the `LICENSE` file in the source tarball (thanks nonamedotc)

* 28 Upgrade to `isort` 5.
* 27 Test the `plys` entry point loads correctly.
* 29 Set `python_requires` in `setup.cfg`.

* 25 Fix tests now `Document.workspace` is a required argument (thanks betaboon).
* 23 and 26 Move package metadata to `setup.cfg` (thanks KOLANICH).

* 21 Fix bug where `target_version` is missing for projects without a config file (thanks fsouza).

* 20 Upgrade to `black` version `19.3b0`:
* Drops support for `--skip-numeric-underscore-normalisation` / `skip_numeric_underscore_normalisation`
* Deprecates support for `--py36` / `py36`
* Adds support for `--target-version` / `target_version` (supersedes deprecated `py36` option)
* Thanks to extraymond and nasyxx

* Add Python 3.7 classifier to `setup.py`.