oiiotool - split help message into separate function
oiiotool - split help message into separate function

bdeluca/oiio,mcanthony/oiio,mcanthony/oiio,lgritz/oiio,micler/oiio,OpenImageIO/oiio,lgritz/oiio,micler/oiio,bdeluca/oiio,YangYangTL/oiio,OpenImageIO/oiio,YangYangTL/oiio,OpenImageIO/oiio,lgritz/oiio,bdeluca/oiio,micler/oiio,YangYangTL/oiio,bdeluca/oiio,mcanthony/oiio,mcanthony/oiio,micler/oiio,OpenImageIO/oiio,YangYangTL/oiio,lgritz/oiio