Fetch Jsonp Versions Save

MR https://github.com/camsong/fetch-jsonp/pull/68

Thanks to @stfsy

https://github.com/camsong/fetch-jsonp/pull/67

Thanks to @timothy-bailey-redbox

Thanks to @tanzhangwen https://github.com/camsong/fetch-jsonp/pull/57

Thanks the idea from @doxiaodong

Handle <script> error event, thanks to @michaelvial

• Remove global export of fetchJsonp

• Format code
• Update Readme