* Improved unknown handling
* Configure option `CLICON_YANG_DIR` is changed from a single directory to a path of directories
* Note CLIXON_DATADIR (=/usr/local/share/clixon) need to be in the list
* Names lexically correct (NCName)
* Syntactically Correct handling of '<?' (processing instructions) and '<?xml' (XML declaration)
* XML prolog syntax for 'well-formed' XML
* <!DOCTYPE (ie DTD) is not supported.
This affects installations where the libraries are installed outside
the normal library search paths (e.g. FreeBSD puts ports libraries
in /usr/local/lib by default, which is not on the default lib path)