Fix indentation. Update doxygen comments

include/sta/gpio_pin.hpp

@@ -8,28 +8,39 @@
 
 namespace sta
 {
-	/**
-	 * @brief GPIO pin state.
-	 */
-	enum class GpioPinState
-	{
-		LOW,
-		HIGH
-	};
+    /**
+     * @defgroup sta_core_gpio GPIO
+     * @ingroup sta_core
+     * @brief GPIO pins.
+     * @{
+     */
 
-	/**
-	 * @brief Interface for GPIO pins.
-	 */
-	class GpioPin
-	{
-	public:
-		/**
-		 * @brief Set pin output state.
-		 *
-		 * @param state     Output state
-		 */
-		virtual void setState(GpioPinState state) = 0;
-	};
+
+    /**
+     * @brief GPIO pin state.
+     */
+    enum class GpioPinState
+    {
+        LOW,
+        HIGH
+    };
+
+    /**
+     * @brief Interface for GPIO pins.
+     */
+    class GpioPin
+    {
+    public:
+        /**
+         * @brief Set pin output state.
+         *
+         * @param state     Output state
+         */
+        virtual void setState(GpioPinState state) = 0;
+    };
+
+
+    /** @} */
 } // namespace sta