Sphinx's "autoprogram" fails to parse docstrings containing a section header.
"autoprogram" starts nested parsing with empty `memo.title_styles` and a
`<section>` as root node. In this context, the "root section" should be
considered a "level 0" section.
Remove the unattached "root section" from the list of `parent_sections` so that
appending a new top-level section to `parent_sections[0].parent` works.