Nest all namespaces

The compiler supports this now.  We can type less going forward.
No functional changes.

Signed-off-by: Stephan Pleines <pleines.stephan@gmail.com>
Change-Id: I29d6fa4f9aacc0e381f1a7637294db0392466995
diff --git a/y2016/actors/superstructure_actor.cc b/y2016/actors/superstructure_actor.cc
index d33b125..734512a 100644
--- a/y2016/actors/superstructure_actor.cc
+++ b/y2016/actors/superstructure_actor.cc
@@ -8,8 +8,7 @@
 #include "y2016/control_loops/superstructure/superstructure_goal_generated.h"
 #include "y2016/control_loops/superstructure/superstructure_status_generated.h"
 
-namespace y2016 {
-namespace actors {
+namespace y2016::actors {
 
 namespace chrono = ::std::chrono;
 
@@ -112,5 +111,4 @@
   WaitUntil(::std::bind(&SuperstructureActor::SuperstructureDone, this));
 }
 
-}  // namespace actors
-}  // namespace y2016
+}  // namespace y2016::actors