Add React-Native Support

[n3tr]

resolve #34

• Create Native-specific extension file to export unstable_batchedUpdates function from react-native package
  • https://facebook.github.io/react-native/docs/platform-specific-code#native-specific-extensions-ie-sharing-code-with-nodejs-and-web
• Check for browser variables window and document
• I tried to add example for react-native as part of this repo but unable symlink the package locally (probably due to Haste or duplicated react copy). Thus, I created a separated repo for demo and testing instead.
  • Demo: https://github.com/n3tr/ReactNativeSWRExample

https://github.com/n3tr/ReactNativeSWRExample/blob/master/App.js#L5-L14

[shuding]

Thank you so much!