declaring the lv_group_remove_all_objs function.

src/lv_core/lv_group.h

@@ -113,6 +113,12 @@ void lv_group_add_obj(lv_group_t * group, lv_obj_t * obj);
  */
 void lv_group_remove_obj(lv_obj_t * obj);
 
+/**
+ * remove all objects from a group
+ * @param group pointer to a group
+ */
+void lv_group_remove_all_objs(lv_group_t * group);
+    
 /**
  * Focus on an object (defocus the current)
  * @param obj pointer to an object to focus on