Support `setext` style md headings in menu item parsing

[MrArnoldPalmer]

Parsing md headers from the readme + api reference into a packages navigation items currently does not support setext style headings. This causes these items to not be displayed in the left nav of a package page.

[github-actions[bot]]

This issue is now marked as stale because it hasn't seen activity for a while. Add a comment or it will be closed soon.

[addihorowitz]

@MrArnoldPalmer do you have an example you can share so that it will be easy to reproduce and resolve?

[MrArnoldPalmer]

settext headings are detailed in the github flavored markdown specification. As far as we know there is no package currently on construct-hub that uses them, and this should be superceded by a migration to a JSON format from jsii-docgen.

[github-actions[bot]]

This issue is now marked as stale because it hasn't seen activity for a while. Add a comment or it will be closed soon. If you wish to exclude this issue from being marked as stale, add the "backlog" label.