Added find and variants to ustring
Added find and variants to ustring

mcanthony/oiio,sambler/oiio,jeremyselan/oiio,scott-wilson/oiio,cwilling/oiio,cwilling/oiio,sambler/oiio,cwilling/oiio,sambler/oiio,OpenImageIO/oiio,mcanthony/oiio,OpenImageIO/oiio,scott-wilson/oiio,lgritz/oiio,OpenImageIO/oiio,bdeluca/oiio,micler/oiio,mcanthony/oiio,YangYangTL/oiio,lgritz/oiio,lgritz/oiio,YangYangTL/oiio,OpenImageIO/oiio,scott-wilson/oiio,mcanthony/oiio,cwilling/oiio,micler/oiio,YangYangTL/oiio,jeremyselan/oiio,sambler/oiio,YangYangTL/oiio,jeremyselan/oiio,bdeluca/oiio,lgritz/oiio,scott-wilson/oiio,bdeluca/oiio,bdeluca/oiio,micler/oiio,micler/oiio