fix `overrideDefault` and `preventDefault`'s business logic

1. when `preventDefault` runned the method switch to `setDefaultReturn` method
2. cancle switch `overrideDefualt` method to `returnFalseFunc` when it runned once
3. add  switch `overrideDefualt` method to `returnFalseFunc` when `preventDefault` has runned
change README.md and add CHANGLOG.md
move `preReturn` param to `Event.prototype`
finish Event.prototype's code