feature: log level on kprintf (color)

fix: kprintf now uses concatenated strings for the flag

src/debug/print_stack.c

@@ -7,7 +7,7 @@ void print_stack(void)
 	    (struct stackframe *)__builtin_frame_address(0);
 
 	while (stack) {
-		kprintf(0, "fn: %d\n", stack->eip);
+		kprintf(KERN_DEBUG "fn: %d\n", stack->eip);
 		stack = stack->ebp;
 	}
 }