add support for blockquote alerts #42
Description
GFM added support for alerts in blockquotes.
- https://github.blog/changelog/2023-12-14-new-markdown-extension-alerts-provide-distinctive-styling-for-significant-content/
- https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#alerts
> [!NOTE]
> Useful information that users should know, even when skimming content.
> [!TIP]
> Helpful advice for doing things better or more easily.
> [!IMPORTANT]
> Key information users need to know to achieve their goal.
> [!WARNING]
> Urgent info that needs immediate user attention to avoid problems.
> [!CAUTION]
> Advises about risks or negative outcomes of certain actions.