Merge remote-tracking branch 'origin/2.9'

* origin/2.9:
  docs: apply some bugfixes from master to writing-tests.adoc
  mux_generic: remove includes of unused header files
  Added new file code/writing-tests.adoc to set of translated files.
  Document how to run and write tests

Author: SebKuzminsky

src/hal/components/mux_generic.c

@@ -20,12 +20,7 @@
 #include "rtapi.h"
 #include "rtapi_app.h"
 #include "hal.h"
-#include "hal_priv.h"
 
-#if !defined(__KERNEL__)
-#include <stdio.h>
-#include <stdlib.h>
-#endif
 
 /* module information */
 MODULE_AUTHOR("Andy Pugh");