cannot refer to anchors in SUMMARY.md

[christian-posta]

when adding the "anchors" plugin, I cannot seem to refer to an anchor in one of the docs listed in my SUMMARY.md.

For example, I have a long markdown file with different sections; would be great to link to them from the summary file like this:

* [Section of title](api/index.md#section-title-here)

[scottdorman]

This would be very useful for me as well. I have different files for each of the "top level" sections, but I'd like to have the TOC show all of the sections in each file and have them be links. Right now, the best I've been able to do is get them to show up but only the top level section is a clickable link.