Pyscaffoldext-markdown

* Switch to [`myst-parser`](https://pypi.org/project/myst-parser/) from `recommonmark`, PR #16
* Added badges to the `README.md` template, PR 21
* Remove description section in `README.md`, PR 39
* Add a static `CONTRIBUTING.md` template, PR 27

- Latest updates from PyScaffold
- Fix issue with kebab-cased-keys in `setup.cfg`, PR 13
- Fix issue of dsproject extension `KeyError: 'long-description'`, issue 20

- Changes required for PyScaffold v4.0
- Updated system tests/CI using `pyscaffoldext-custom-extension`
- Simplified templates package thanks to `pyscaffold.templates.get_template`
- Removed unnecessary `coding: utf-8` comments
- Use symlinks to load `README.md`, `AUTHORS.md`, `CHANGELOG.md` into Sphinx, issues 6, 7.

- Fix wrong `long-description` in `setup.cfg`
- Remove deprecated `enable_auto_doc_ref` option
- Remove deprecated `source_parsers`

- Some cosmetics

- Changes necessary for PyScaffold 3.2
- Regenerated extension using `--custom-extension`
- Several cleanups