cligen

Added new nodetest and treeref-flags callbacks to be able to skip commands dynamically

Compilation fix from previous commit

Fixed: [cli description should be enumeration's desc not the leaf's. for yang enum type](https://github.com/clicon/clixon/issues/183)

Exported history functions to be called from upper layer (clixon)

Fixed: [Inconsistent error messages for out of range values](https://github.com/clicon/clixon/issues/567)