Dedicated xml,json,yang and xsl parser utility programs added

Sanity check of stdarg (...) added
Cleanup of error messages.

test/test_yang_parse.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+# Test: XML parser tests
+PROG=../lib/src/clixon_util_yang
+
+# include err() and new() functions and creates $dir
+. ./lib.sh
+
+YANG=$(cat <<EOF
+module test{
+   prefix ex;
+   extension c-define {
+      description "Example from RFC 6020";
+      argument "name";
+   }
+   ex:not-defined ARGUMENT;
+}
+EOF
+)
+
+new "yang parse"
+expecteof $PROG 0 "$YANG" "^$YANG$"
+
+rm -rf $dir
+