threshold of quadratic and linear growth of CLIgen buffers (cbuf:s)
* Memory footprint
* Do not autopopulate namespace cache, instead use on-demand, see `xml2ns()`.
* Set CBUF start level to 256 (`CLICON_CLI_BUF_START` option)
* Reduced xml child vector default size from 4 to 1 with quadratic growoth to 64K then linear
* C-code changes:
- Replaced stream uri:s w constants
- Replaced large debug print code with single clicon_log_xml
- Restconf put and post handling refactored using new parse API
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
* If you retrieve state _and_ config data using RESTCONF or NETCONF `get`, a severe performance penalty occurs if you have large lists (eg ACLs). Workaround: disable `VALIDATE_STATE_XML` in `include/clixon_custom.h`.
* From a cli perspective this is a revert to 4.1 behaviour, where the cli does not immediately exit on start if the backend is not running, but with the new session-id function
* From a cli perspective this is a revert to 4.1 behaviour, where the cli does not immediately exit on start if the backend is not running, but with the new session-id function
