doxygen compilation issues

[kb1hyr]

System is ubuntu 20.04, though I am not sure its important.

After ./configure, make stops with an error when doxygen reports that there is no @return for functions that are defined as static void and no @param for functions with void parameter. If you add those, clang reports these as an error later in the process. Problem is resolved (i.e. compilation is accomplished) when WARN_AS_ERROR is changed from YES to NO in doc.cfg. I'm not really great with this stuff, so I am reporting this in case there is a more elegant way (i.e. a different flag to be set in doc.cfg) so it isn't expecting @return & @param for voids. Great work!