Investigate performance

[geowurster]

As indicated by pypa/setuptools#510, pkg_resources is known to be slow. click-plugins leverages setuptools entry points to load CLI plugin commands but this comes with a performance hit for the entire CLI application. I don't think there is anything to be done about it directly but it is worth documenting the behavior and trying fast-entry_points.

[BlinkyStitt]

importlib_metadata.entry_points() is also faster than pkg_resources.

[geowurster]

See #40 for details about the future of this project.