plugins exts CHANGE ext parsing isolated into a callback

Lots of refactoring and finishing up included.
diff --git a/src/log.h b/src/log.h
index 6afd2e7..f1fde4c 100644
--- a/src/log.h
+++ b/src/log.h
@@ -1,9 +1,10 @@
 /**
  * @file log.h
  * @author Radek Krejci <rkrejci@cesnet.cz>
+ * @author Michal Vasko <mvasko@cesnet.cz>
  * @brief Logger manipulation routines and error definitions.
  *
- * Copyright (c) 2015 - 2018 CESNET, z.s.p.o.
+ * Copyright (c) 2015 - 2022 CESNET, z.s.p.o.
  *
  * This source code is licensed under BSD 3-Clause License (the "License").
  * You may not use this file except in compliance with the License.