Add a :maxdepth: option to all toctree directives to limit their depth
to 1. We do not want subheadings from individual documents to pollute
the already large lists of CMake Domain objects.
Add the man page description line as explicit markup at the top of each
Help/manual/*.rst file and scan it from conf.py to automatically
generate the man_pages Sphinx configuration value. This reduces the
number of places that need to be changed when a new manual is added.
It designed to search for implementation of backtrace(3) routine.
Currently it is used in OpenBSD Ports for building Clementine
music player.
A lot of input from brad.king@ and neundorf@.