doc: fix and complemented some doxygen headers

sys/include/chardev_thread.h

@@ -11,6 +11,12 @@
  * @defgroup    sys_chardevthread Chardev Thread
  * @ingroup     sys
  * @brief       Chardev thread
+ * @{
+ *
+ * @file
+ * @brief       Handles I/O from a char devices
+ *
+ * @author      Kaspar Schleiser <kaspar@schleiser.de>
  */
 
 #ifndef __CHARDEV_THREAD_H
@@ -30,3 +36,4 @@ void *chardev_thread_entry(void *rb_);
 #endif
 
 #endif /* __CHARDEV_THREAD_H */
+/** @} */

sys/include/crypto/sha256.h

@@ -28,12 +28,6 @@
  */
 
 
-/**
- * @defgroup    sys_sha256 SHA264
- * @ingroup     sys
- * @brief       SHA264 hash generator
- */
-
 /**
  * @ingroup     sys_crypto
  * @{

sys/include/ps.h

@@ -11,6 +11,12 @@
  * @defgroup    sys_ps PS
  * @ingroup     sys
  * @brief       Show list with all threads
+ * @{
+ *
+ * @file
+ * @brief       List information about all active threads
+ *
+ * @author      Kaspar Schleiser <kaspar@schleiser.de>
  */
 
 #ifndef __PS_H
@@ -28,3 +34,4 @@ void _ps_handler(int argc, char **argv);
 #endif
 
 #endif /* __PS_H */
+/** @} */

sys/include/random.h

@@ -11,6 +11,10 @@
  * @defgroup    sys_random Random
  * @ingroup     sys
  * @brief       Random number generator
+ * @{
+ *
+ * @file
+ * @brief       Mersenne Twister - a very fast random number generator
  */
 
 #ifndef RANDOM_H
@@ -85,3 +89,4 @@ double genrand_res53(void);
 #endif
 
 #endif /* RANDOM_H */
+/** @} */