Very large commit for upcoming 4.4 release

Major New features

* New and updated search functions using xpath, api-path and instance-id
  * New search functions using api-path and instance_id:
    * C search functions: `clixon_find_instance_id()` and `clixon_find_api_path()`
  * Binary search optimization in lists for indexed leafs in all three formats.
    * This improves search performance to O(logN) which is drastical improvements for large lists.
  * You can also register explicit indexes for making binary search (not only list keys)
  * For more info, see docs at [paths](https://clixon-docs.readthedocs.io/en/latest/paths.html) and
[search](https://clixon-docs.readthedocs.io/en/latest/xml.html#searching-in-xml)

API changes on existing features (you may need to change your code)
* On failed validation of leafrefs, error message changed from: `No such leaf` to `No leaf <name> matching path <path>`.
* CLI Error message (clicon_rpc_generate_error()) changed when backend returns netconf error to be more descriptive:
  * Original: `Config error: Validate failed. Edit and try again or discard changes: Invalid argument`
  * New (example): `Netconf error: application operation-failed Identityref validation failed, undefined not derived from acl-base . Validate failed. Edit and try again or discard changes"

Minor changes

* Test framework
  * Added `-- -S <file>` command-line to main example to be able to return any state to main example.
  * Added `test/cicd` test scripts for running on a set of other hosts
* C-code restructuring
  * clixon_yang.c partitioned and moved code into clixon_yang_parse_lib.c and clixon_yang_module.c and move back some code from clixon_yang_type.c.
    * partly to reduce size, but most important to limit code that accesses internal yang structures, only clixon_yang.c does this now.

lib/src/clixon_json_parse.y

@@ -2,7 +2,7 @@
  *
   ***** BEGIN LICENSE BLOCK *****
  
-  Copyright (C) 2009-2019 Olof Hagsand and Benny Holmgren
+  Copyright (C) 2009-2020 Olof Hagsand
 
   This file is part of CLIXON.
 
@@ -245,7 +245,7 @@ json_current_body(struct clicon_json_yacc_arg *jy,
 */
 
  /* top: json -> value is also possible */
-json          : value J_EOF { clicon_debug(2,"json->object"); YYACCEPT; } 
+§json          : value J_EOF { clicon_debug(2,"json->object"); YYACCEPT; } 
               ;
 
 value         : J_TRUE  { json_current_body(_JY, "true");}