Pymdown-extensions

- **NEW**: Require Python Markdown 3.6+.
- **FIX**: Fix some test cases.
- **FIX**: Fix warnings due to recent changes in Python Markdown.

- **FIX**: SmartSymbols: Ensure symbols are properly translated in table of content tokens.

- **NEW**: Emoji: Update Twemoji and Gemoji data to latest.
- **NEW**: Emoji: Due to recent Gemoji update, non-standard emoji are no longer indexed. So emoji such as `:octocat:`
are no longer resolved.
- **NEW**: Highlight: Added new option `default_lang` which will cause code blocks with no language specifier to be
highlighted with the specified default language instead of plain text. This affects indented code blocks and code
blocks defined with SuperFences.
- **NEW**: InlineHilite: `style_plain_text` can be specified with a language string (in addition to its previous
boolean requirement) to treat inline code blocks with no explicit language specifier with a specific default
language.

- **NEW**: MagicLink: Allow configuring custom repository providers based off the existing providers.

- **NEW**: Blocks: Admonitions and Details now allow configuring custom block classes and default titles.
- **FIX**: Keys: Ensure that Keys does not parse base64 encoded URLs.

- **NEW**: Snippets: Allow PathLike objects for `base_path` to better support interactions with MkDocs.
- **FIX**: Block Admonitions: Empty titles should be respected.
- **FIX**: Block Details: Empty summary should be respected.