TypeDesc: Beef up doxygen-like comments (#2245)
TypeDesc: Beef up doxygen-like comments (#2245)

Also re-jigger some of the constructors to make them a little compact
by more liberally using default argument values and delegated
constructors.
lgritz/oiio,OpenImageIO/oiio,lgritz/oiio,OpenImageIO/oiio,OpenImageIO/oiio,lgritz/oiio,OpenImageIO/oiio,lgritz/oiio