Move all floats to doubles

The code was developed initially around a pid loop implemented using
floats.  Therefore, the code was converting back and forth between
double for sensor values as inputs and outputs from this PID loop.

Change-Id: I2d2919e1165103040729c9f16bb84fde3dd6b81b
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/pid/pidcontroller.cpp b/pid/pidcontroller.cpp
index cbe2452..7be6ceb 100644
--- a/pid/pidcontroller.cpp
+++ b/pid/pidcontroller.cpp
@@ -28,9 +28,9 @@
 
 void PIDController::process(void)
 {
-    float input;
-    float setpt;
-    float output;
+    double input;
+    double setpt;
+    double output;
 
     // Get setpt value
     setpt = setptProc();