Include all children in HTML for breadcrumbs and directory listings

[isaacwhite]

These can be hidden to start, but would be nice for the full tree to at least be exposed to the templates so that customizations could change the display format.

Would be nice at the same time to consider adding config options for the depth of TOC modules, which could be build to an arbitrary depth in our parsing code but are currently capped at h2s.

Part of #213