Generate .ipynb for <example> sections in API reference docs

[dsyme]

Currently the fsdocs tool generates an .ipynb for every literate script of markdown file if a _template.ipynb is present (it can be an empty file).

We could also easily generate .ipynb for API reference docs. That is fsdocs could generate a notebook for each "" section from the XML docs, and optionally add a mybinder link for each example. Then all API docs would be easily made executable

[Fxplorer]

include .dib