Added interface iRotaryAngle

Signed-off-by: Stefan Andritoiu <stefan.andritoiu@gmail.com>

include/interfaces/iProximity.hpp

@@ -34,6 +34,11 @@ namespace upm
   public:
     virtual ~iProximity() {}
 
+    /**
+     * Get proximity value from sensor data.
+     *
+     * @return Proximity value as volts.
+     */
     virtual float getValue() = 0;
   };
 }