Added doxyfile (doxygen) for the common folder. Started with doxygen comments for app and tft module.

common/app/app.h

@@ -1,2 +1,30 @@
+/**
+ * @defgroup app Application
+ * The App Module contains the effective, platform independent application.
+ */
+
+
+/**
+ * @addtogroup app
+ */
+/*@{*/
+
+/**
+ * Starts/Initializes the app
+ * This function should be called at the top of the main function of your platform
+ */
 void app_init();
+
+/**
+ * Executes one cycle of the app
+ * Call this function repeatedly from a loop inside the main function
+ */
 void app_process();
+
+/**
+ * @defgroup screens Screens
+ * The Screens of the application. \sa Screen
+ */
+
+
+/*@}*/