Adds automagically generating libvncserver/libvncclient API
    documentation using doxygen. This gives a nice overview on both APIs,
    include dependencies and function call/caller dependencies.

    TODO: Modify all the explaining comments in the .c files for use with
          doxygen as well.

    This patch only changes comments, no functional changes at all!
Signed-off-by: Christian Beier <dontmind@freeshell.org>