API docs: web: adjust frontend to render new backend data format

Created by: slimsag

requires a few frontend changes to faithfully render. This is those changes.

This isn't a final form, it's just a stepping stone with approximately the same frontend as what we had before. The cool/new things will come later.

The main change here is that subpages now have a dedicated index section:

Signed-off-by: Stephen Gutekanst [email protected]