To generate Doxygen documentation for the C++ code,
just make sure you have doxygen installed
(ubuntu package name is "doxygen"),
cd to this directory, then issue command 
"doxygen" without arguments.

HTML documentation will be created in directory "html"
under this directory. The top level file
of the documentation will be "html/index.html".
Point your browser to that to see the documentation.

Latex documentation will also be created in directory "latex".
To also generate PDF documentation, "cd latex; make pdf".
The pdf file is refman.pdf.

For readability, the C++ code does not contain
and Doxygen directives, so the generated documentation
will only contain what Doxygen can do with "EXTRACT_ALL=YES"
and without relying on documentation directives in the code.
Even with this limitation, this can be very useful to explore the C++ code.

The Doxygen documentation is too large to be added
to the git repository, and so the top level 
.gitignore ignores docs/doxygen/html.
