structure FEATURE support for augment-structure

WIP
diff --git a/src/plugins_exts.h b/src/plugins_exts.h
index 298557c..2c264a7 100644
--- a/src/plugins_exts.h
+++ b/src/plugins_exts.h
@@ -102,7 +102,7 @@
 /**
  * @brief Extensions API version
  */
-#define LYPLG_EXT_API_VERSION 5
+#define LYPLG_EXT_API_VERSION 6
 
 /**
  * @brief Macro to define plugin information in external plugins