Sopel-help

Hotfix for the release 0.5, because we can't really expect people to have `pkg_resources` available (in particular when we don't have the dependency declared properly). So instead, we use `importlib_metadata`, at least until we drop support for Python 3.9 (see also 11).

Thank you dgw for the hotfix!

Hotfix for the previous release, apparently something changed in how setuptools manage a `package.find` option so, it has to be fixed for this release.

In preparation of Sopel upcoming 8.0 release, sopel-help gets a bit of housekeeping:

* remove support for Python 3.7 (9)
* modernize project's packaging (good bye `setup.py`, welcome `pyproject.toml`) (9)
* bug fix: no more empty line (7)

This is the first release where sopel-help lose features:

* ubuntu provider has been removed, as the online service is made for human only usage, not automated tools such as Sopel
* hastebin provider has been removed, as the service has been acquired by an untrusted third party

On the plus side:

* sopel-help now requires Sopel 7.1+ and Python 3.7+
* sopel-help is now compatible with Sopel 8, allowing future improvement

For this third release (beta) of `sopel-help`, two new little quality of life improvements:

* `.h` is now a shortcut for `.help`
* the local HTML help generator now generate link & anchor to each plugin name

Thanks to our contributors!

This second release (still in beta) of `sopel-help` brings a new feature: the number of lines of help message that can be sent to a channel is now configurable. By default, it's still 3.

The best way to configure the plugin is to use the official cli tool:

sopel-plugins configure help

Don't forget to use the `-c` option if needed.

This new feature has automated tests to ensure everything work as intended.

Compatible with Python 3.5+ and Sopel 7+ only.