Major overhaul:

- transition to `pyproject.toml` config
- include license (Apache-2.0)
- add dev tools
- add documentation config (`mkdocs` based)
- turn `README.md` into a symlink to docs `index.md`
- add convenience scripts for testing and linting

.gitignore

@@ -1,10 +1,25 @@
 # Python virtual environment:
-/.venv/
+/.venv*/
+/venv*/
+/.env*/
+/env*/
+
 # IDE settings:
 /.idea/
 /.vscode/
-# Distribution / packaging:
+
+# Distribution / build files:
 *.egg-info/
 /dist/
-# Python cache:
+/docs/build/
+/site/
+
+# Python cache / compiled files:
 __pycache__/
+*.py[cod]
+
+# Testing:
+/.coverage
+
+# mypy:
+.mypy_cache/