v2022.6.20 — Date releases, versioningit, et alii

- Give `pyrepo release` a `--date` flag
- Give `pyrepo begin-dev` a `--no-next-version` flag
- `pyrepo release`: Don't upload projects with "Private" classifiers to PyPI
- Support projects that use versioningit
    - Add a `uses_versioningit: bool` template variable
- Support CHANGELOG headers of the form `vDATEVERSION`
- Update for setuptools 61.0.0
- Update twine dependency to 4.0
- Templates:
    - Update `sphinx-copybutton` version to `~=0.5.0`
    - Update `.readthedocs.yml` to use a `build:` section and rename the file to `.readthedocs.yaml`
    - Update `.pre-commit-config.yaml`
    - Update `Sphinx` version to `~=5.0`
    - `setup.cfg`: Use `find_namespace:` instead of `find:` (See <pypa/setuptools#3340>)
- Internal API:
    - Store project details in a `ProjectDetails` class
    - Add `Templater` and `TemplateWriter` classes
    - Include classifiers in project details

CHANGELOG.md

@@ -1,5 +1,5 @@
-In Development
---------------
+v2022.6.20
+----------
 - Give `pyrepo release` a `--date` flag
 - Give `pyrepo begin-dev` a `--no-next-version` flag
 - `pyrepo release`: Don't upload projects with "Private" classifiers to PyPI