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/y2014/control_loops/drivetrain/drivetrain_base.cc b/y2014/control_loops/drivetrain/drivetrain_base.cc
index be4f238..d9f396e 100644
--- a/y2014/control_loops/drivetrain/drivetrain_base.cc
+++ b/y2014/control_loops/drivetrain/drivetrain_base.cc
@@ -13,8 +13,7 @@
 
 namespace chrono = ::std::chrono;
 
-namespace y2014 {
-namespace control_loops {
+namespace y2014::control_loops {
 
 const DrivetrainConfig<double> &GetDrivetrainConfig() {
   // TODO(austin): Switch over to using the profile.
@@ -51,5 +50,4 @@
   return kDrivetrainConfig;
 };
 
-}  // namespace control_loops
-}  // namespace y2014
+}  // namespace y2014::control_loops