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.
This commit helps reduce clutter on the navigation sidebar.
Creates new directories and moves relevant files into them.
Modifies index.rst, symlinks, and image paths accordingly.
This commit also enables expandable/collapsible navigation items,
renames files in docs/development and docs/production,
modifies /tools/test-documentation so that it overrides a theme setting,
Also updates links to other docs, file paths in the codebase that point
to developer documents, and files that should be excluded from lint tests.
Note that this commit does not update direct links to
zulip.readthedocs.io in the codebase; those will be resolved in an
upcoming follow-up commit (it'll be easier to verify all the links
once this is merged and ReadTheDocs is updated).
Fixes#5265.
Tim Abbott
Axel Tietje
Greg Price
David Rosa Tamsen