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/test/pid_stepwisecontroller_unittest.cpp b/test/pid_stepwisecontroller_unittest.cpp
index 880864d..e3c4f09 100644
--- a/test/pid_stepwisecontroller_unittest.cpp
+++ b/test/pid_stepwisecontroller_unittest.cpp
@@ -24,7 +24,7 @@
     initial.positiveHysteresis = 2.0;
     initial.reading[0] = 20.0;
     initial.reading[1] = 30.0;
-    initial.reading[2] = std::numeric_limits<float>::quiet_NaN();
+    initial.reading[2] = std::numeric_limits<double>::quiet_NaN();
     initial.output[0] = 40.0;
     initial.output[1] = 60.0;
 
@@ -59,7 +59,7 @@
     initial.positiveHysteresis = 2.0;
     initial.reading[0] = 20.0;
     initial.reading[1] = 30.0;
-    initial.reading[2] = std::numeric_limits<float>::quiet_NaN();
+    initial.reading[2] = std::numeric_limits<double>::quiet_NaN();
     initial.output[0] = 40.0;
     initial.output[1] = 60.0;