Add support for inline anchors in Markdown parsing

[Mpdreamz]

Introduced a parser for inline anchors using $$$ syntax and updated related components to handle and render them as HTML anchor tags. Enhanced heading slug generation to exclude inline anchors, and added comprehensive tests to ensure correct behavior.

this is regular text and this $$$is-an-inline-anchor$$$ and this continues to be regular text

will emit:

<p>this is regular text and this <a id="is-an-inline-anchor"></a> and this continues to be regular text</p>

Since this is an inline leaf it can be nested in all markdown container constructs.