Support AsciiDoc Table of Content (ToC) links

Summary

ToC links used to render anchors that when clicked on would move to that section

Steps to reproduce

Create an .adoc file with a ToC:

= {subject}: PREPARED FOR - Gitlab
Adrian Bradshaw <adrian.bradshaw@gmail.com>
:subject: Example Doc
:description:  For troubleshooting ToC link isses
:doctype: book
:confidentiality: Open
:customer: GitLab
:listing-caption: Listing
:toc:
:toclevels: 6

== First section

=== The start 

Live example at: https://gitlab.home.adrians.computer/abradshaw/asciidoc-demo/blob/master/readme.adoc

What is the current bug behavior?

Anchors aren't rendered

What is the expected correct behavior?

ToC links should take you to the section you've clicked on

Relevant logs and/or screenshots

https://gitlab.zendesk.com/agent/tickets/71377