When upgrading from doxygen 1.5.x to 1.8.5 the way the documentation
is generated has underwent many changes, particularly in the headers.
* Change: In <header.html>, must include the javascripts <jquery.js>
    and <dynsections.js>.
* In <CMakeLists.txt>, as the header is customized, doxygen seems not
    copy some files like the javascripts and some images (open.png,
    closed.png). So we copy them from doxygen installation and make
    the CMakeLists.txt install them. I hope they will not change too
    much in the future.
* In <doxyfile>, disable markdown support as it do not interpret
    correctly the formating we already adopted (with a left margin
    to put command into). Use HTML_EXTRA_STYLESHEET instead of
    HTML_STYLESHEET. Enable the index (DISABLE_INDEX=NO), for the
    top header. Enable dot for inheritance diagram. Set the
    EXAMPLE_PATH=. to include the synthetic hierarchy.
    Correct the tag inclusion (faulty path in some places).
* In <SoC.css>, create style for the new header generated by doxygen.
* In the documentation, move the synthetic hierarchy into a module.