0.10.0: improve compatibility with other plugins

Warning

Release yanked, since it broke source path resolution. Fixed in 0.10.1.

• Rewrite image embeds in on_page_markdown
  • Breaking change: embed_format no longer provides {img_open} and {img_close}
• Dependency version bumps
• Document functional Docker example
• Nix dev shell for easier development setup
• Linting via Ruff