docs: Documentation update, initial preparation for version 2.1 release

Change-Id: I3694a8791b9540fc1b926a83ff55421b47e0f1e2
diff --git a/utils/trie/detail/multi-type-container.hpp b/utils/trie/detail/multi-type-container.hpp
index f84f860..5f65aa3 100644
--- a/utils/trie/detail/multi-type-container.hpp
+++ b/utils/trie/detail/multi-type-container.hpp
@@ -81,6 +81,6 @@
 } // ndn
 } // ns3
 
-/// @cond include_hidden
+/// @endcond include_hidden
 
 #endif // MULTI_TYPE_CONTAINER_H_