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/xml.h b/src/xml.h
index edf9512..125271f 100644
--- a/src/xml.h
+++ b/src/xml.h
@@ -133,6 +133,13 @@
 LY_ERR lyxml_ctx_peek(struct lyxml_ctx *xmlctx, enum LYXML_PARSER_STATUS *next);
 
 /**
+ * @brief Remove all the namespaces defined in the element recently closed (removed from the xmlctx->elements).
+ *
+ * @param[in] xmlctx XML context to work with.
+ */
+void lyxml_ns_rm(struct lyxml_ctx *xmlctx);
+
+/**
  * @brief Get a namespace record for the given prefix in the current context.
  *
  * @param[in] ns_set Set with namespaces from the XML context.