feat: highlight plugin add support for line start

[Apostolique]

Summary

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Docs
• Build-related changes
• Other, please describe:

If changing the UI/CSS related code, please provide the before/after screenshot:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• Briefly describing what this PR does in the title in Angular Commit Message Conventions, e.g. fix: rebuild when a page is added

This PR makes it possible to start a code block from a different line number.

```js {lineNumbers:true,lineStart:5}
const cry = Array(3).fill('ora').join(' ')
```

To avoid wasting your time, it's best to open a feature request issue first and wait for approval before working on it.

Other information:

Closes #600

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[egoist]

Hi can you update the docs as well? https://saber.land/docs/markdown-features.html