Code fence metadata

[matkoch]

Is the feature request related to a problem

Some markdown renderers support metadata like title and highlighted lines after the start of a code fence. For instance:

```csharp title="foo" {1,4-6,11}

It'd be great to allow using this with MarkdownSnippets.

Describe the solution

It would require some delimiter to separate the snippet id from the metadata. For instance:

<!-- snippet: xyz -- metadata: title="foo" {...} -->

Describe alternatives considered

No alternatives I presume.

Additional context

No additional context.

[matkoch]

Absolutely no pressure on this, but do let me know if you want a pull-request to outline a solution.

[SimonCropp]

yep happy to accept a PR