sensors/zones: place in namespace and cleanup

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I527dbc8477a232945f696227a7b0b2adbee45175
diff --git a/pid/stepwisecontroller.cpp b/pid/stepwisecontroller.cpp
index c72d61a..e8eb344 100644
--- a/pid/stepwisecontroller.cpp
+++ b/pid/stepwisecontroller.cpp
@@ -30,6 +30,9 @@
 #include <thread>
 #include <vector>
 
+namespace pid_control
+{
+
 void StepwiseController::process(void)
 {
     // Get input value
@@ -105,3 +108,5 @@
     }
     return;
 }
+
+} // namespace pid_control