Have oiiotool help message list the formats supported.
Have oiiotool help message list the formats supported.

Make it easy to tell from running oiiotool what format support was
included at build time.

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