when run `next` method the query will complate one time
Change the cycle way, delete `getAvailableFuncData` method, streamline the code
Optimization `Event` Class

1. Move `next` method to `Event`'s prototype
2. `preventDefault` method add `defReturn` param
`Event` Class add `setDefaultReturn` method
`Event` add `overrideDefault` method
split code into `util.js`
add Asynchronous Mode

`Event` add `async` method to switch query into asynchronous mode
finishing `emit` method's global variables
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
change CHANGELOG.md format
fast merage exporting file
Merge branch 'dev' of https://github.com/Bacra/tEmitter.js into dev
fix `overrideDefault` method. add change `setDefaultReturn` prototype into it
when defCall is not defined and run defCall, reset defaultReturn and preReturn to undefined
rename 'defaultReturn' to 'defReturn', 'setDefaultReturn' to 'setDefReturn'
fix async mode

1. fix emit method return value when async mode is running
2. fix async mode cycle
3. `Event` add `isInAsync` param
`Event` rename `off` to `offSelf` and add `on` `off` `once` method.