add kill + example code

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

kernel/syscall/stub.h

@@ -16,7 +16,7 @@ enum class ID : size_t {
     SEM_SIGNAL=7,
     SYS_GETPID = 8,
     SYS_EXIT = 9,
-    //SYS_KILL=10
+    SYS_KILL = 10
 };
 }  // namespace Syscall
 
@@ -67,3 +67,7 @@ extern "C" ssize_t sys_safe_call(Syscall::ID id, size_t p1, size_t p2,
     sys_call(Syscall::ID::SYS_EXIT, 0, 0, 0, 0, 0);
 }
 
+[[gnu::always_inline]] static inline void sys_kill(size_t pid){
+    sys_call(Syscall::ID::SYS_KILL, pid, 0, 0, 0, 0);
+}
+