Automatic H2 level ToC entry discovery

Docnet will automatically add all H2 (## marked) headers to the ToC as sub navigation elements below a page ToC item. It will automatically add anchors to these H2 headers in the HTML output for the page as well. This makes it very easy to create a fine-grained ToC for easy discovery.

This behavior can be overridden by the MaxLevelInToC configuration option.