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

common/app/screen_filetest.h

@@ -1,3 +1,22 @@
 #include "screen.h"
 
+/**
+ * @addtogroup screens
+ */
+/*@{*/
+
+/**
+ * @defgroup filetest Filetest
+ * The File-Test Screen tests the filesystem module. It read/writes from/to files and shows a bitmap
+ */
+/*@{*/
+
+
+/**
+ * Returns a pointer to the filetest screen
+ * \sa gui_screen_navigate
+ * @return
+ */
 SCREEN_STRUCT* get_screen_filetest();
+
+/*@}@}*/