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/controller.hpp b/pid/controller.hpp
index bf79937..5530843 100644
--- a/pid/controller.hpp
+++ b/pid/controller.hpp
@@ -15,9 +15,9 @@
 {
     virtual ~Controller() = default;
 
-    virtual float inputProc(void) = 0;
+    virtual double inputProc(void) = 0;
 
-    virtual void outputProc(float value) = 0;
+    virtual void outputProc(double value) = 0;
 
     virtual void process(void) = 0;