plugins ext FEATURE initial schema-mount support

Only for XML data for now. Includes lots of other
changes needed to support this extension.
diff --git a/src/plugins_exts/metadata.c b/src/plugins_exts/metadata.c
index 2313090..bc70694 100644
--- a/src/plugins_exts/metadata.c
+++ b/src/plugins_exts/metadata.c
@@ -161,10 +161,10 @@
 
         .plugin.id = "libyang 2 - metadata, version 1",
         .plugin.compile = &annotation_compile,
-        .plugin.parse = NULL,
-        .plugin.validate = NULL,
         .plugin.sprinter = &annotation_schema_printer,
-        .plugin.free = annotation_free
+        .plugin.free = annotation_free,
+        .plugin.parse = NULL,
+        .plugin.validate = NULL
     },
     {0}     /* terminating zeroed record */
 };