curl_multi_strerror - return string describing error code
       #include <curl/curl.h>
       const char *curl_multi_strerror(CURLMcode errornum);
       The  curl_multi_strerror()  function  returns  a  string describing the
       CURLMcode error code passed in the argument errornum.
       This function was added in libcurl 7.12.0
       A pointer to a zero terminated string.
       libcurl-errors(3), curl_easy_strerror(3), curl_share_strerror(3)