Unable to link using `xref:` syntax to command pages

[ronaldtse]

Pages like this: docs/commands/control-flow/if.adoc

Have a snippet like this:

=== See Also

* xref:../ifelse.adoc[`ifelse`] - Two-way conditional
* xref:../loop.adoc[`loop`] - Indefinite repetition
* xref:../stopped.adoc[`stopped`] - Error catching
* Comparison operators: `eq`, `ne`, `lt`, `le`, `gt`, `ge`
* Boolean operators: `and`, `or`, `not`

However, these links xref:../ifelse.adoc[...] do not render as properly to
/docs/commands/control-flow/ifelse/ but instead to
/docs/commands/control-flow/ifelse.html.

And on GitHub Pages, this results in a 404 error. The correct link should be to
/docs/commands/control-flow/ifelse/.

This task is to fix these links throughout the documentation so that they use
the correct xref: syntax that resolves to the proper permalink structure.