Import referenced documents at build time

Added import references, restoring and improving the functionality of the ‘transclude’ reference that I previously deprecated and removed.

Has two modes, both of which support comments.

import, transcludes the content of the referenced document as is, without any additional markup or visual cue.
aside, creates an aside-type block that also includes an outbound link.

Both support an optional comment at the reference-site that is discarded during substitution.

The following snippet (minus the backslash),

  {{ aside::501108be#getting arrested again }\}

Would be substituted with this markup,

  {.aside}
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
The first time you get arrested your friends ask you, "What happened?!"\
The second time you get arrested it's already, "What did you do?"
`<time class="smallcaps">`{=html}[November  3, 2024 3.13PM ⚕ Istanbul, Turkey](/2024/11/03/151330)`</time>`{=html}
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

Which would then be rendered into the following later in the build,

The first time you get arrested your friends ask you, “What happened?!”
The second time you get arrested it’s already, “What did you do?” November 3, 2024 3.13PM ⚕ Istanbul, Turkey

Both forms of import create a backlink in the referenced document, but only aside creates a visible outward link at the reference-site. This allows documents to be assembled seamlessly where that is a better fit than a call-out, but generally I expect I’ll use the aside mode more often, as I generally prefer for connections to be bi-directional.