feature: support line number in code blocks

[egoist]

Feature request

What problem does this feature solve?

Show line numbers in code blocks.

What does the proposed API look like?

Globally enabled:

markdown:
  lineNumbers: true

Toggle line numbers per code block:

```js {lineNumbers:true}
console.log(42)
```

How should this be implemented in your opinion?

Implement it in the markdown/highlight-plugin.js

Are you willing to work on this yourself?

If no one else will.

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[krmax44]

@lubien Don't forget to grab your bounty at Issuehunt 😄

[lubien]

@krmax44 Oh, yea. I think it has some delay time because it's pending so I'm just waiting.

[IssueHuntBot]

@egoist has rewarded $28.00 to @lubien. See it on IssueHunt

• 💰 Total deposit: $40.00
• 🎉 Repository reward(20%): $8.00
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