PDF reference manual suggestions
Currently the main TOC has only one level, which works well for the HTML output, but not for the PDF output. Perhaps we need a different top-level rst file in the two cases.
Also, 60 pages of release notes probably isn't needed; prefer a comment that the release notes are available online.
Change toctree depth in PDF manual
It doesn't seem to be possible to set different toctree depths for the
HTML and PDF versions of the manual in Sphinx itself. To work around
this, I added the explicit depth to the LaTeX preamble.