Support for data-line-numbers

[amannn]

Reveal.js is able to highlight individual lines in code blocks. It would be great if reveal-md would support this with a syntax like this:

```js {2}
const foo = 'foo';
const bar = 'bar'; // I'm highlighted

[webpro]

Hi @amannn! That looks like an interesting feature, and I like the syntax. Feel free to open a pull request :)

[amannn]

Ok, I'll see if I can some time to implement it!

[niweb21]

Hi @amannn, this feature already works in reveal-md 🙂 https://revealjs.com/markdown/#syntax-highlighting

```js [1-2|2]
const foo = 'foo';
const bar = 'bar'; // I'm highlighted

@webpro Do you want a chapter in the readme ?

[amannn]

True, that works for me – thanks @niweb21!

[webpro]

Hi @amannn, this feature already works in reveal-md 🙂 https://revealjs.com/markdown/#syntax-highlighting

```js [1-2|2]
const foo = 'foo';
const bar = 'bar'; // I'm highlighted

@webpro Do you want a chapter in the readme ?

That would be great! Thanks for posting the solution here as well, much appreciated :)