Imu improvements

Write tests for IMU, pass them.

This MR has little to contribute to Master apart from IMU, but there are a few little impros.

src/examples/processor_imu.yaml

@@ -5,4 +5,5 @@ keyframe vote:
     max buffer length:  20000    # motion deltas
     dist traveled:      2.0   # meters
     angle turned:       0.2   # radians (1 rad approx 57 deg, approx 60 deg)
-    voting_active:      false
+    voting_active:      false
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+    
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