w-level general upgrades and as a complement to module-specific upgrade.
* Called on startup after initial XML parsing, but before module-specific upgrades
* Enabled by definign the `.ca_datastore_upgrade`
* [General-purpose upgrade documentation](https://clixon-docs.readthedocs.io/en/latest/backend.html#ge
neral-purpose)
* JSON parse error messages change from ` on line x: syntax error,..` to `json_parse: line x: syntax err
or`
* Unknown-element error message is more descriptive, eg from `namespace is: urn:example:clixon` to: `Fai
led to find YANG spec of XML node: x with parent: xp in namespace urn:example:clixon`.
* C-API parse and validation API more capable
* `xml_spec_populate` family of functions extended with three-value return values
* -1: error, 0: parse OK, 1: parse and YANG binding OK.
* `xml_parse` and `json_parse` API changes
* Three value returns: -1: error, 0: parse OK, 1: parse and YANG binding OK.
* Extended `xml_parse_file2` and `xml_parse_string2` extended API functions with all options available.
* New concept called `yang_bind` that defines how XML symbols are bound to YANG after parsing
* Existing API same except `xml_parse_file` `endtag` argument moved to `xml_parse_file2`
* C-API: Added instrumentation: `xml_size` and `xml_stats_get`.
* Fixed: Enabling modstate (CLICON_XMLDB_MODSTATE), changing a revision on a yang, and restarting made the backend daemon exit at start (thanks Matt)
* Also: ensure to load `ietf-yang-library.yang ` if CLICON_XMLDB_MODSTATE is set
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.
