Markdown-customblocks

- map: fix: Geocoding failed because now requires user agent

- Fixed documentation link in metadata

- Empty release to solve packaging problems

- Dropped support for Python<3.8
- Use backslash \ to continue the headline on the next line
- New `figure` attributes:
- `inline`: embeds the image as base64 encoded
- `local`: turns a remote url image into a relative local resource
- `thumb`: reduces the size of the image, enlargeable by clicking
- Dropped support for Python<3.8
- Migrated to pyproject
- Upgrade notes:
- Image recommended css for lightbox has changed to enable thumbnailing

- Documentation corrections

- Third party generators can be registered by using project
metadata's entry points for `markdown.customblocks.generators`
- New block types
- `wikipedia`: produces a linkcard for a lemma
- `mastodon`: embed a mastodon post
- `peertube`: embed a peertube video
- `linkcard`:
- Keyless values are added as classes to the top level element
- Extract descriptions from MediaWiki based sites (wikipedia...)
- Html class `squared` renamed `side`, used to identify side images
- Configurable CSS variables in the recommended stylesheet
- Improved image layout in the recommended styleshet
- Side image turns wide image on small devices
- `vimeo`:
- Wrapping inside `div.video.vimeo` analog to other video inserts
- Accepts exceding key and positional parameters like `container`
- `youtube`:
- Fix: iframe border removed by default