src: Changing namespace ndn to namespace nfd

Also, this commit imports used classes from ::ndn namespace (from
NDN-CPP library) directly to ::nfd namespace.

refs: #1163

Change-Id: I9cc9d72e00af495b4ed0c84e6d418a7c9ba986cb
diff --git a/daemon/face/face.hpp b/daemon/face/face.hpp
index f014545..d6da710 100644
--- a/daemon/face/face.hpp
+++ b/daemon/face/face.hpp
@@ -10,7 +10,7 @@
 #include "common.hpp"
 #include "util/event-emitter.hpp"
 
-namespace ndn {
+namespace nfd {
 
 /** \class FaceId
  *  \brief identifies a face
@@ -85,6 +85,6 @@
   std::string m_description;
 };
 
-} // namespace ndn
+} // namespace nfd
 
 #endif // NFD_FACE_FACE_H