GitLab

* Apply blacken-docs and fix language-hints

* Add blacken-docs pre-commit hook

* Add pycln pre-commit hook

* Enable a few builtin hooks

* Black no longer ignores pyi files

* Apply isort

* Tweak isort config

* Add env.py as a known_first_party

* Add one missing known first party

* Make config compat with older isort versions

* Add another comment

* Revert pyproject setting

* fix: chapters in PDF again

* fix: sections in README

* docs: fix PDF build by adding unicode mappings

* fix: better PDF

* fix: html build issue

* style: use Black everywhere

* style: minor touchup from review

* feat: import check as a common function

* docs: add cmake to docs

* docs: read version from pybind11 file

* docs: show full PEP 440 version everywhere

* Doxygen needs `RECURSIVE = YES` in order to parse the `detail` subdir.

* The `-W` warnings-as-errors option for sphinx doesn't work with the
  makefile build. Switched to calling sphinx directly.

* Fix "citation [cppimport] is not referenced" warning.

* Make 'any' the default markup role for Sphinx docs

* Automate generation of reference docs with doxygen and breathe

* Improve reference docs coverage

The missing empty line after `.. code-block::` resulted in incorrectly
parsed restructuredtext (sphinx warnings) and the code blocks were not
generated in the html output.

The `exclude_patterns` change just silences the orphaned file warning.

[ci skip]