feat: support GFM-style alerts in Markdown

[mcdurdin]

From #952.

See: https://github.com/orgs/community/discussions/16925

[mcdurdin]

This has to be added as a extension to Parsedown, which is the Markdown renderer that we use.

https://github.com/orgs/community/discussions/16925 shows the styles we are aiming for, let's stick with those.

There may be a feature in Parsedown that does this for us, I haven't looked.

[mcdurdin]

For reference, this is what we are looking for!

[Meng-Heng]

@mcdurdin, I don't think Parsedown has this feature yet.

• A request for Alerts support: https://github.com/erusev/parsedown/issues/860
• Latest Parsedown releases do not mention the Alerts feature: https://github.com/erusev/parsedown/releases
• Other markdown renderers start supporting Alerts upon the User's request: https://github.com/jgm/commonmark-hs/issues/132
• Parsedown's demo page:
  

I also don't see this feature being added to their v2.0.0 roadmap.

[mcdurdin]

@Meng-Heng, we'd need to write this as an extension. Parsedown has a tutorial on writing extensions: https://github.com/erusev/parsedown/wiki/Tutorial:-Create-Extensions

It might be worth reading links erusev/parsedown#860 as well.

If this seems a bit too deep, no worries, we can postpone this and come back to it later

[Meng-Heng]

Thank you @mcdurdin,
I have started a composer project on Wednesday so I would like to take a look through the links you sent and see how much I can go from there.