* 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.
* Except `CLICON_RESTCONF_DIR` which remains in clixon-config.yang due to bootstrapping
* -d <dir> option removed
* This applies to both evhtp and fcgi RESTCONF
* Both can also read config from backend, and be started from backend
* You may need to move config as follows (from clixon-config.yang to clixon-restconf.yang)
* CLICON_RESTCONF_PRETTY -> restconf/pretty
* CLICON_RESTCONF_PATH -> restconf/fcgi-path
* Not backward compatible: All uses of the ca-auth callback in restconf plugins must be changed
* New version is: `int ca_auth(h, req, auth_type, authp, userp)`
* where `auth_type` is the requested authentication-type (none, client-cert or user-defined)
* `authp` is the returned authentication flag
* `userp` is the returned associated authenticated user
* and the return value is three-valued: -1: Error, 0: ignored, 1: OK
* For more info see [clixon-docs](https://clixon-docs.readthedocs.io/en/latest/restconf.html)
* New clixon-restconf@2020-12-30.yang revision
* 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)
* NACM recovery user session is now properly enforced. This means that if `CLICON_NACM_CREDENTIALS` is `except` (default), then a specific `CLICON_NACM_RECOVERY_USER` can make any edits and bypass NACM rules.
* If a default value is replaced by an actual value, RESTCONF return values have changed from `204 No Content` to `201 Created`
* clixon-config.yang: Removed default valude of CLICON_NACM_RECOVERY_USER
