add kill + example code

scheduler.kill seems like its not implemented comletly or doest work as
expected.

kernel/user/app1/appl.cc

@@ -1,20 +1,7 @@
 // vim: set noet ts=4 sw=4:
-
 #include "appl.h"
 #include "../../syscall/stub.h"
 
-#include "../../arch/core.h"
-#include "../../arch/system.h"
-#include "../../debug/output.h"
-#include "../../device/textstream.h"
-#include "../../interrupt/guard.h"
-#include "../../sync/semaphore.h"
-#include "../../thread/scheduler.h"
-extern Semaphore koutsem;
-extern TextStream kout;
-
-extern Application apps[];
-
 void Application::action() {  // NOLINT
 	// Thread 1 may be an auxiliary thread