sensors/zones: place in namespace and cleanup

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I527dbc8477a232945f696227a7b0b2adbee45175
diff --git a/pid/pidcontroller.hpp b/pid/pidcontroller.hpp
index fd41c09..cb92377 100644
--- a/pid/pidcontroller.hpp
+++ b/pid/pidcontroller.hpp
@@ -8,6 +8,9 @@
 #include <memory>
 #include <vector>
 
+namespace pid_control
+{
+
 class ZoneInterface;
 
 /*
@@ -63,3 +66,5 @@
     std::string _id;
     double lastInput = std::numeric_limits<double>::quiet_NaN();
 };
+
+} // namespace pid_control