Added support to adding simple block rules

[KostyaTretyak]

const marked = require('marked');
const blockStr = `
# Example usage with embed block code

@@@ gist
a9dfd77500990871fc58b97fdb57d91f.js
@@@

@@@ youtube
JgwnkM5WwWE
@@@
`;

marked.setBlockRule(/^@@@ *(\w+)\n([\s\S]+?)\n@@@/, function (execArr) {
  const channel = execArr[1];
  switch (channel) {
    case 'youtube': {
        const id = marked.escape(execArr[2]);
        return `<iframe width="420" height="315" src="https://www.youtube.com/embed/${id}"></iframe>\n`;
     }
    case 'gist': {
        const id = marked.escape(execArr[2]);
        return `<script src="https://gist.github.com/${id}"></script>\n`;
     }
  }
});
const html = marked.parse(blockStr);
console.log(html);

Output:

<h1 id="example-usage-with-embed-block-code">Example usage with embed block code</h1>
<script src="https://gist.github.com/a9dfd77500990871fc58b97fdb57d91f.js"></script>
<iframe width="420" height="315" src="https://www.youtube.com/embed/JgwnkM5WwWE"></iframe>

[joshbruce]

Thanks @KostyaTretyak! Gonna flag this for milestone 0.5.0. If you could take a look at #1002 - I believe it could cause this to have merge conflicts in the future as we would need to add tests to document and validate the solution works. Cheers.

[KostyaTretyak]

@joshbruce no, it does not seem that my changes were in conflict with the changes introduced in #1002.

[Feder1co5oave]

shouldn't this be 'simpleRule' + i ?

[KostyaTretyak]

Yes, you are right, I'll correct it right now. Thank you.

[joshbruce]

See #1026

Closing as merge conflicts - also building out the issue above to consolidate ideas and approaches proposed.