* Previous support did no validation of values.
* Validation of types and CLI expansion
* Example extended with inclusion of iana-if-type RFC 7224 interface identities
* CLICON_NACM_MODE config option, default is disabled.
* Added username attribute to all rpc:s from frontend to backend
* Added NACM backend module in example
* Backend RPC register callback function (Netconf RPC or restconf operation POST) has been changed from: `backend_rpc_cb_register()` to `rpc_callback_register()`
* Backend RPC callback signature has been changed from: `int cb(clicon_handle h, cxobj *xe, struct client_entry *ce, cbuf *cbret, void *arg)` has been changed to : `int cb(clicon_handle h, cxobj *xe, struct client_entry *ce, cbuf *cbret, void *arg)`
* Frontend netconf and restconf plugins can register callbacks as well with same API as backends.
* Builds and installs a new restconf library: libclixon_restconf.so and clixon_restconf.h
* The restconf library can be included by a restconf plugin.
* Example code in example/Makefile.in and example/restconf_lib.c
* Authorization
* Example extended with authorization
* Test added with http basic authorization (test/test_auth.sh)
* Documentation in FAQ.md
* README.md extended with new yang, netconf, restconf, datastore, and auth sections.
statements and identifying them as extensions or not. However,
semantics for specific extensions must still be added.
* Renamed ytype_id and ytype_prefix to yarg_id and yarg_prefix, respectively
* Added cli_show_version()
