New API is as follows:
* `clixon_xml2file()` - Print internal tree as XML to file
* `clixon_xml2cbuf()` - Print internal tree as XML to buffer
* `clixon_json2file()` - Print internal tree as JSON to file
* `clixon_json2cbuf()` - Print internal tree as JSON to buffer
* `clixon_cli2file()` - Print internal tree as CLI format to file
* `clixon_txt2file()` - Print internal tree as text format to file
* `clixon_netconf_error(category, xerr, msg, arg)` removed first argument -> `clixon_netconf_error(xerr, msg, arg)`
* Renamed utility function `clixon_util_insert()` to `clixon_util_xml_mod()` and added merge functionality.
* Fixed: Insertion of subtree leaf nodes were not made in the crrect place, always ended up last regardless of yang spec (if ordered-by system).
