name: allow negative argument for 'get' method to get component from the back

Change-Id: I7e76fc16dfc5ce8ed2a18cfb461f884b82e1b274
diff --git a/include/ndn-cpp/name.hpp b/include/ndn-cpp/name.hpp
index 132def5..633593c 100644
--- a/include/ndn-cpp/name.hpp
+++ b/include/ndn-cpp/name.hpp
@@ -582,7 +582,13 @@
    * @return The name component at the index.
    */
   const Component& 
-  get(size_t i) const { return components_[i]; }
+  get(ssize_t i) const
+  {
+    if (i >= 0)
+      return components_[i];
+    else
+      return components_[size() + i];
+  }
   
 
   const Component&