Added basic rfc8527 support, but without support for:
* ds:operational
* with-origin
* clixon/test/test_rfc8527_*.sh
The current level of rfc8527 support is intended to allow commit
operations on the 'candidate' datastore without rewriting the 'startup'
datastore.
Added documentation in comments in test scripts, added example site.sh,
moved evaluation of site.sh later in lib.sh to allow site.sh to override
more lib.sh variables.
* The existing autocli does not support modes, complete paths must be given, eg: `set a b c d 42`.
* In the new auto-cli, automatic modes are present at each YANG syntax node level, eg the above can be given as: `edit a b c; set d 4; top`
* The existing CLI API remains, the new API is as follows: `cli_auto_edit()`, `cli_auto_up()`, `cli_auto_top()`, `cli_auto_show()`, `cli_auto_set()`, `cli_auto_merge()`, `cli_auto_create()`, `cli_auto_del()`.
* See `test/test_cli_auto.sh` for an example of the new API, and `apps/cli/cli_auto.c` for the source code of the new callback API.
* Documentation will be appear and full integration with the main example.
* Added inline state field to clixon-example.yang
* Added new clicon_data_cvec_*() API for generic cvec structs
* A new configuration option `CLICON_CONFIGDIR` has been added for loading of extra config files
* If not given, only the main configfile is loaded.
* If given, and if the directory exists, the files in this directory will be loaded alphabetically AFTER the main config file in the following way:
* leaf values are overwritten
* leaf-list values are appended
* You can override file setting with `-E <dir>` command-line option.
* New clixon-config@2020-10-01.yang revision
* Added option for configuration directory: `CLICON_CONFIGDIR`
* `count`, `name`, `contains`, `not`, as defined in [xpath 1.0](https://www.w3.org/TR/xpath-10)
* `deref`, `derived-from` and `derived-from-or-self` from RFC7950 Section 10.
* in particular in augment/when statements
* Improved error handling
* Verification of XPath functions is done at startup when yang modules are loaded, not when XPaths are evaluated.
* Separation of "not found" and "not implemented" XPath functions
* Both give a fatal error (backend does not start).
