long firestring_vfprintfe(FILE * stream, struct firestring_estr_t *format, va_list ap)
DESCRIPTION
firestring_vfprintfe() behaves exactly like
firestring_vfprintf(3)
except that it takes an estring format argument, so the
format can contain arbitrary binary data. However, please
note that user user-input data as the format string is
INSECURE.