Zensical support

[analog-cbarber]

Eventually want to port similar functionality, if not this exact plug-in to Zensical

see https://zensical.org/compatibility/#phased-transition-strategy

In the meantime, you can enable compatibility checking introduced in version 2.1.0 to
convert your cross-references to be compatible with the standard handler's cross-reference
support.

Also note: mkdocstrings/python#328