Add pytest to dev dependencies;

upgrade dev dependencies;
remove unnecessary main test script entrypoint;
remove unnecessary line from `.gitignore`;
put repo description variable into top-level `__init__.py`;
introduce syntax-error as a reminder to fix copyright;
add CSS fix for broken inline-code segments;
update `index.md` layout;
reorder linting script calls and add a bit more output;
support Python 3.8+ by default;
fix wrong dependency file reference in `pyproject.toml`;
add `pytest` config to `pyproject.toml`;
call `pytest` in `coverage` config;
add a few sensible rule-ignores to `ruff` config

requirements/dev.txt

@@ -1,9 +1,10 @@
 -r full.txt
-black==23.9.1
+black==23.10.1
 build==1.0.3
 coverage[toml]==7.3.2
 isort==5.12.0
 mkdocs-material==9.4.6
 mkdocstrings[python]==0.23.0
 mypy==1.5.1
-ruff==0.0.292
+pytest==7.4.3
+ruff==0.1.3