* Experimental text syntax parser/loader

* 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)

test/test_helloworld.sh

@@ -133,8 +133,8 @@ ret=$($clixon_cli -1 -f $cfg show config)
 if [ $? -ne 0 ]; then
     err 0 $r
 fi  
-if [ "$ret" != "hello     world;" ]; then
-    err "$ret" "hello     world;"
+if [ "$ret" != "clixon-hello:hello     world;" ]; then
+    err "$ret" "clixon-hello:hello     world;"
 fi
 
 new "netconf edit-config"