apds9930: enable sensor before read out sensor data

Changes in library:
- enableProximity() function is to enable or disable proximity sensor
- enableIlluminance() function is to enable or disable illuminance sensor
- run clang-format

Changes in example:
- proximity and illuminance kernel IIO-based driver init state is power off,
  require enable before read out sensor data. Sleep time is needed after
  enable, the sleep time may vary on different platform.
- run clang-format

Signed-off-by: Lay, Kuan Loon <kuan.loon.lay@intel.com>
Signed-off-by: Mihai Tudor Panu <mihai.tudor.panu@intel.com>

src/apds9930/apds9930.hpp

@@ -1,6 +1,6 @@
 /*
  * Author: Lay, Kuan Loon <kuan.loon.lay@intel.com>
- * Copyright (c) 2015 Intel Corporation.
+ * Copyright (c) 2016 Intel Corporation.
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -75,6 +75,16 @@ class APDS9930
      * @return Proximity value
      */
     int getProximity();
+    /**
+     * Enable proximity
+     * @param enable state
+     */
+    bool enableProximity(bool enable);
+    /**
+     * Enable illuminance
+     * @param enable state
+     */
+    bool enableIlluminance(bool enable);
 
   private:
     mraa_iio_context m_iio;