Reconsider page.extra.top

[ShawnPConroy]

See: aaranxu#18

Currently, this marks the page as one where the next/previous link should go up to a parent section. But it does weird stuff there, and this is not fully compatible.

Currently, it may break some expected functionality since it won't go to the first page of a subsection of a parent, which is a weird thing to do.

Perhaps it should just default to go up to a parent or a parent's parent when all subsections are done.