基本核心模組的init與exit

http://blog.xuite.net/mb1016.flying/linux/25695797-%E5%9F%BA%E6%9C%AC%E6%A0%B8%E5%BF%83%E6%A8%A1%E7%B5%84%E7%9A%84init%E5%8F%8Aexit