* Fixed multi-namespace for augmented state which was not covered in 4.2.0.
* The multi-namespace augment state may rearrange the XML namespace attributes.
* Mandatory variables can no longer be deleted.
RFC 8040 Sec 3.1
* non-pretty print remove all spaces, eg `{"operations":{"clixon-example:client-rpc":[null]`
* Replaced JSON `null` with `[null]` as proper empty JSON leaf/leaf-list encoding.
* [Cannot write to config using restconf example #91](https://github.com/clicon/clixon/issues/91)
* Updated restconf documentation (the example was wrong)
* [clixon-lib yang revision file name update #92](https://github.com/clicon/clixon/issues/92)
* Clixon-lib yang file had conflicting filename and internal yang revision.
* This was only detected in the use-case when a whole dir was loaded.
* Inserted sanity check in all yang parse routines.
* Committed updated clixon-lib yang file that triggered the error
* Restconf RFC 8040 increased feature compliance
* Cache-Control: no-cache added in HTTP responses (RFC Section 5.5)
* Restconf monitoring capabilities (RFC Section 9.1)
* Added support for Yang extensions
* New plugin callback: ca_extension
* Main backend example includes example code on how to implement a Yang extension in a plugin.
* JSON changes
* Non-pretty-print output removed all extra spaces.
* Example: `{"nacm-example:x": 42}` --> {"nacm-example:x":42}`
* Empty JSON container changed from `null` to `{}`.
* Empty list and leafs remain as `null`
* Removed unnecessary configure dependencies
* libnsl, libcrypt, libm, if_vlan,...
* pseudo-plugin added, to enable callbacks also for main programs. Useful for extensions
* Yang Unique statements with multiple schema identifiers did not work on some platforms due to memory error.
* Validate-only transactions are terminated by an `end` or `abort` callback.
* If a commit user callback fails, a new `revert` callback will be made to plugins that have made a succesful commit.
