* Hello message semantics has been made stricter according to RFC 6241 Sec 8.1, for example:
* A client MUST send a <hello> element.
* Each peer MUST send at least the base NETCONF capability, "urn:ietf:params:netconf:base:1.1" (or 1.0 for RFC 4741)
* The netconf client will terminate (close the socket) if the client does not comply
* You can set `CLICON_NETCONF_HELLO_OPTIONAL` to true to use the old behavior of essentially ignoring hellos.
* New clixon-config@2020-03-08.yang revision
* Added: `CLICON_NETCONF_HELLO_OPTIONAL`
* The base capability has been changed to "urn:ietf:params:netconf:base:1.1" following RFC6241.
* Replaces the hardcoded "config" keyword.
* Implemented by a compile-time option called `DATASTORE_TOP_SYMBOL` option in clixon_custom.h
* Tests: added endtest to all tests. Removed all premature exits if BE=0
* Only requests on the form: `<rpc xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"><edit-config>...` will be accepted
* All replies will be on the form: `<rpc-reply xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">...`
* Requests such as: `<rpc><edit-config>...` will not be accepted.
* You can revert this behaviour (to clixon pre-4.6 behaviour) by enabling `CLICON_NAMESPACE_NETCONF_DEFAULT`
* This API change is a consequence of: [copy-config's RPC cxobj parameter does not contain namespace #131](https://github.com/clicon/clixon/issues/131)
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
