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/frc971/control_loops/flywheel/flywheel_controller.cc b/frc971/control_loops/flywheel/flywheel_controller.cc
index dc82147..aa8087f 100644
--- a/frc971/control_loops/flywheel/flywheel_controller.cc
+++ b/frc971/control_loops/flywheel/flywheel_controller.cc
@@ -3,9 +3,8 @@
 #include <chrono>
 
 #include "aos/logging/logging.h"
-namespace frc971 {
-namespace control_loops {
-namespace flywheel {
+
+namespace frc971::control_loops::flywheel {
 
 // Class to current limit battery current for a flywheel controller.
 class CurrentLimitedStateFeedbackController
@@ -173,6 +172,4 @@
 
 double FlywheelController::velocity() const { return loop_->X_hat(1, 0); }
 
-}  // namespace flywheel
-}  // namespace control_loops
-}  // namespace frc971
+}  // namespace frc971::control_loops::flywheel