/** @file @brief Checks whether a string follows correct library.dataset format @details Many macros in the core library accept a library.dataset parameter referred to as 'libds'. This macro validates the structure of that parameter, eg: @li 8 character libref? @li 32 character dataset? @li contains a period? It does NOT check whether the dataset exists, or if the library is assigned. Usage: %put %mf_islibds(work.something)=1; %put %mf_islibds(nolib)=0; %put %mf_islibds(badlibref.ds)=0; %put %mf_islibds(w.t.f)=0; @param [in] libds The string to be checked @return output Returns 1 if libds is valid, 0 if it is not