Added doxgen comments to filesyste, checkbox, numupdown and screen module. And some minor changes to the other modules.

common/lowlevel/ll_system.h

@@ -1,7 +1,29 @@
 #include <stdbool.h>
 #include <stdint.h>
 
+
+/**
+ * @defgroup lowlevel LowLevel
+ * The Low-Level platform abstraction layer
+ */
+/*@{*/
+
+/**
+ * @defgroup ll_system System (LowLevel)
+ * Low level functions of the \ref system Module
+ */
+
+/*@}*/
+
+/**
+ * @addtogroup ll_system
+ */
+/*@{*/
+
+
 bool ll_system_init();
 void ll_system_delay(uint32_t msec);
 void ll_system_process();
 void ll_system_toggle_led();
+
+/*@}*/