Always add toc to Markdown Class Instance
Always add toc to Markdown Class Instance

Previously, we only added the toc attribute (md.toc) if no Marker was
found within the document. However, that has caused framworks to do things
like force insert a marker, run convert, then extract the toc from the
body of the document. This is much cleaner. And if the user wants to add
the toc to the document also, they still can.

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