Referring to a term defined within document with automatic anchors

[ronaldtse]

In #154 this syntax was implemented:

=== Term defined within current document

If the term is defined within the current document, the term citation
gives the anchor of the term definition in the document, the canonical
term name, and optionally the text to be displayed.

The anchor is converted into a document crossreference in the Metanorma XML.

The syntax is:

[source,adoc]
----
{{local-anchor,term}}

// if the display text differs from the cited term
{{local-anchor,term,text}}
----

In metanorma/metanorma-iso#369 , the automatic term anchors were defined -- but only in ISO.

We should create the term lookup table in standoc, not only ISO.

Then we can do:

----
{{term}}

// if the display text differs from the cited term
{{term,text}}
----

[ronaldtse]

This has been implemented as smart terms references by @opoudjis across flavors . Closing.