The commit adds a new config value 'texinfo_emit_document_references'
that blocks the emission of inline references and make it better readable
with legacy stand-alone reader ``info``.

Before the change we emit:
Default option value for @ref{e,,-Wshift-overflow3}.

while with texinfo_emit_document_references == True:
Default option value for -Wshift-overflow3.

It addresses limitations mentioned in Sphinx' FAQ:
https://www.sphinx-doc.org/en/master/faq.html#texinfo-info

New Sphinx tutorial, part III

Update description about how `conf.py` is loaded/executed