refine toString
	modified:   src/main.scala
	modified:   src/systemscala/component.scala
	modified:   src/systemscala/event.scala
	modified:   src/systemscala/helper.scala
	modified:   src/systemscala/pipe.scala
	modified:   src/systemscala/signal.scala
	modified:   src/systemscala/simtime.scala
	modified:   src/systemscala/thread.scala