Expression engine: use preprocessor macro for vector mean functions, added vector norm function.
Expression engine: use preprocessor macro for vector mean functions, added vector norm function.

malloch/libmapper,radarsat1/libmapper,radarsat1/libmapper,malloch/libmapper,libmapper/libmapper,radarsat1/libmapper,malloch/libmapper,radarsat1/libmapper,libmapper/libmapper,malloch/libmapper,libmapper/libmapper,radarsat1/libmapper,malloch/libmapper,libmapper/libmapper,libmapper/libmapper,malloch/libmapper,libmapper/libmapper