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/y2020/control_loops/superstructure/turret/aiming.cc b/y2020/control_loops/superstructure/turret/aiming.cc
index 0b2c5f3..238beda 100644
--- a/y2020/control_loops/superstructure/turret/aiming.cc
+++ b/y2020/control_loops/superstructure/turret/aiming.cc
@@ -3,10 +3,7 @@
 #include "y2020/constants.h"
 #include "y2020/control_loops/drivetrain/drivetrain_base.h"
 
-namespace y2020 {
-namespace control_loops {
-namespace superstructure {
-namespace turret {
+namespace y2020::control_loops::superstructure::turret {
 
 using frc971::control_loops::Pose;
 using frc971::control_loops::aiming::RobotState;
@@ -197,7 +194,4 @@
   return builder.Finish();
 }
 
-}  // namespace turret
-}  // namespace superstructure
-}  // namespace control_loops
-}  // namespace y2020
+}  // namespace y2020::control_loops::superstructure::turret