Remove several section spec subsections from the table of contents.
Review Request #11703 — Created July 6, 2021 and submitted
This switches the "Examples", "Options", "Metadata Keys", and
"Subsections" in the DiffX Sections page to use
.. rubric::instead of
an actual section. This keeps these out of the Table of Contents,
cleaning that up considerably and solving some issues with upcoming
changes that add actual, useful subsections alongside these.
Built the docs. Checked the rubric-based subsections to make sure they
were no longer showing up in the Table of Contents.