Escape special chars in docs

[wcmonty]

When generating documentation {bar} in the documentation triggers a warning like:

asciidoctor: WARNING: skipping reference to missing attribute: bar

This is part of the the reason for this issue in the Rubocop repository (although there are other places that this can be seen in other Rubocop repositories).

To test:

# Generate documentation on current master
# We receive some warnings during generation
rubocop-ast git:(wm/escape_references_in_docs) > git checkout master
Switched to branch 'master'
Your branch is up to date with 'origin/master'.
rubocop-ast git:(master) > asciidoctor -a attribute-missing=warn docs/modules/ROOT/pages/node_types.adoc -o master.html
asciidoctor: WARNING: skipping reference to missing attribute: bar
asciidoctor: WARNING: skipping reference to missing attribute: bar
asciidoctor: WARNING: skipping reference to missing attribute: bar
asciidoctor: WARNING: skipping reference to missing attribute: bar
asciidoctor: WARNING: skipping reference to missing attribute: bar

# Generate documentation on the fix branch
rubocop-ast git:(master) > git checkout wm/escape_references_in_docs
Switched to branch 'wm/escape_references_in_docs'
Your branch is up to date with 'origin/wm/escape_references_in_docs'.
rubocop-ast git:(wm/escape_references_in_docs) > asciidoctor -a attribute-missing=warn docs/modules/ROOT/pages/node_types.adoc -o escaped.html

# We can see that the only difference between the generated files is the timestamp
rubocop-ast git:(wm/escape_references_in_docs) > diff master.html escaped.html
1601c1601
< Last updated 2021-07-02 12:39:33 -0400
---
> Last updated 2021-07-02 12:39:46 -0400

[marcandre]

Great, thanks!