Refactor and modernize namespace declarations

 * Completely remove inline namespace v2
 * Flatten some unnecessarily deep namespace nesting
 * Move DummyClientFace, Segmenter, SegmentFetcher to namespace ndn
 * Move all unit tests to namespace ndn::tests

Change-Id: I8bcfcf9fd669936a3277d2d5d505f765b4b05742
diff --git a/docs/release-notes/release-notes-0.2.0.rst b/docs/release-notes/release-notes-0.2.0.rst
index 5d804bf..89d7c08 100644
--- a/docs/release-notes/release-notes-0.2.0.rst
+++ b/docs/release-notes/release-notes-0.2.0.rst
@@ -66,7 +66,7 @@
   + Introduce ``util::EventEmitter``, :ndn-cxx:`util::NotificationSubscriber`,
     :ndn-cxx:`util::NotificationStream`, and :ndn-cxx:`nfd::FaceMonitor` utility classes
 
-  + Introduce :ndn-cxx:`util::SegmentFetcher` helper class to fetch multi-segmented data
+  + Introduce :ndn-cxx:`SegmentFetcher` helper class to fetch multi-segmented data
     (:issue:`1879`)
 
 - **Build**