Added support for list x y;
Uses a mechanism to parse as unknown XML body and post-parsing replace with list keys
Fixed example and test to work with new TEXT syntax
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
* Added new text syntax parsing and loading from CLI
* Unified text output functions to `xml2txt` and moved to clixon_text_syntax.[ch]
* The following are removed: `cli_xml2txt` and `xml2txt_cb`
* Text output format changed:
* Namespace/modulename added to top-level
* See [Support performant load_config_file(...) for TEXT format](https://github.com/clicon/clixon/issues/324)
