New version of pandoc-include-doc: inclusion of single elements of an external document

[massifrg]

There's a new version of pandoc-include-doc.

The new feature is the inclusion of single blocks (or inlines) of another document, instead of the whole document.
The selection of included elements is by identifier or class, so you can only include Blocks and Inlines that have an Attr.
Anyway you can extend it to other elements, just surrounding them with a Div or a Span with a certain id or class.

For people interested in sub-document inclusion, see also include-files, referred in #11377, which has a less verbose syntax.