add support for size_t flag: %zd

printf.c

@@ -425,6 +425,10 @@ static size_t _vsnprintf(char* buffer, size_t buffer_len, const char* format, va
       flags |= FLAGS_LONG_LONG;
       format++;
     }
+    if ((*format == 'z')) {
+        flags |= (sizeof(size_t) == 8 ? FLAGS_LONG_LONG : FLAGS_LONG);
+        format++;
+    }
 
     // evaluate specifier
     switch (*format) {