Child pages

[vadimkantorov]

Hi!

I'm trying to fix support for child pages.

There is structured_notion['pages'][block['id']]['url'] which fails as child_page's are not registered in the structured_notion['pages'] top-level dict

This fails in practice + there is # "child_page": child_page which hints that child_page rendering was not complete / tested

Also, in my case child_page appears to have children itself, and these seem not rendered at all by the existing impl

Could you please comment on the state of support for child pages? Thanks :)