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.

test/test_xpath_canonical.sh

@@ -63,3 +63,6 @@ new "xpath canonical form (wrong namespace should fail)"
 expectpart "$($clixon_util_xpath -c -y $ydir -p /i:x/j:y -n i:urn:example:c -n j:urn:example:b)" 255
 
 rm -rf $dir
+
+# unset conditional parameters 
+unset clixon_util_xpath