* Pushed tag to 4.0.1.PRE

* Restconf RFC 8040 increased feature compliance
  * Cache-Control: no-cache added in HTTP responses (RFC Section 5.5)
  * Restconf monitoring capabilities (RFC Section 9.1)
* Added support for Yang extensions
  * New plugin callback: ca_extension
  * Main backend example includes example code on how to implement a Yang extension in a plugin.
* JSON changes
  * Non-pretty-print output removed all extra spaces.
    * Example: `{"nacm-example:x": 42}` --> {"nacm-example:x":42}`
  * Empty JSON container changed from `null` to `{}`.
    * Empty list and leafs remain as `null`
* Removed unnecessary configure dependencies
  * libnsl, libcrypt, libm, if_vlan,...
* pseudo-plugin added, to enable callbacks also for main programs. Useful for extensions
* Yang Unique statements with multiple schema identifiers did not work on some platforms due to memory error.

lib/clixon/clixon_json.h

@@ -2,7 +2,7 @@
  *
   ***** BEGIN LICENSE BLOCK *****
  
-  Copyright (C) 2009-2019 Olof Hagsand and Benny Holmgren
+  Copyright (C) 2009-2019 Olof Hagsand
 
   This file is part of CLIXON.
 
@@ -32,6 +32,8 @@
   ***** END LICENSE BLOCK *****
 
  * JSON support functions.
+ * JSON syntax is according to:
+ * http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-404.pdf
  */
 #ifndef _CLIXON_JSON_H
 #define _CLIXON_JSON_H