This is what the Sphinx docs recommend when you actually don't want
the page to be included in navigation:
http://www.sphinx-doc.org/en/stable/markup/toctree.html
And now that we have `eval_rst`, we're able to take advantage of it!
One difference between doing this and the old way of making "hidden"
toctree entries is that with the latter, the "previous" and "next"
links at the bottom of each page would thread through the hidden
entries; which gets kind of confusing when they don't appear in the nav.
Sphinx was displaying "WARNING: document isn't included in any toctree"
for files we just don't want in the TOC. We can hide them from the index,
but the rtd theme defaults to display hidden index entries in the nav bar.
This commit excludes these files from such warnings, and patches layout.html
so that hidden index entries stay hidden from the navigation sidebar.
This commit also moves password-strength.md under docs/production and
adds it as a hidden entry in production/index.rst.
Fixes#7417.
Greg Price
David Rosa Tamsen