Initial move of some wiki contents into main documentation.

This moves some information from the wiki into the main generated doxygen
documenation. It is fairly rought but includes examples for inline and
stand-alone diagrams, linking to external HTML pages, etc.

Among other things, it allows for better cross-referencing into the
main doxygen contents and thus for overall shorter documentation.

Signed-off-by: Jon A. Cruz <jonc@osg.samsung.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Added configure option for documentation build.

Added option with fallback of 'auto' to control building of documentation.

Signed-off-by: Jon A. Cruz <jonc@osg.samsung.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>