Support for Admonition syntax (non-standard)

Please add support for Admonitions!

https://python-markdown.github.io/extensions/admonition/

Admonitions are created using the following syntax:

!!! type "optional explicit title within double quotes"
    Any number of other indented markdown elements.

    This is the second paragraph.

Since I am a mkdocs-material user, it would be really great to have this. Even in a previewer in vscode admonitions are displayed.

[DavidAnson]

The CLI does not currently support markdown-it plugins.

[miffels]

@berot3 @Stanzilla did any of you have luck with what David proposed? I just tried hacking the plugin into the markdownlint-cli options passed to markdownlint, but it doesn’t seem to do anything - markdownlint still interprets paragraphs in admonition as indented code blocks:

!!! note
    This is a note

    Second paragraph, which markdownlint reports as code block :(

@DavidAnson just to confirm - below is what you have been proposing, right?

const markdownItAdmonition = require('markdown-it-admonition');
// ...
// https://github.com/igorshubovych/markdownlint-cli/blob/master/markdownlint.js#L237
const markdownItPlugins = [[markdownItAdmonition]];
  const lintOptions = {
    config,
    customRules,
    files,
    markdownItPlugins
  };
// ...
const lintResult = markdownlint.sync(lintOptions);

If we can get this to work, I’d consider making a PR to have this supported in markdownlint-cli.