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/constants.cc b/y2016/constants.cc
index 707fa9c..0c65b11 100644
--- a/y2016/constants.cc
+++ b/y2016/constants.cc
@@ -21,8 +21,7 @@
 #define M_PI 3.14159265358979323846
 #endif
 
-namespace y2016 {
-namespace constants {
+namespace y2016::constants {
 
 // ///// Mutual constants between robots. /////
 const int Values::kZeroingSampleSize;
@@ -210,5 +209,4 @@
   return *values[team_number];
 }
 
-}  // namespace constants
-}  // namespace y2016
+}  // namespace y2016::constants