* [apple] Move iOS/macOS src into common apple dir

* [apple] Enable macOS as platform in podspec

* [example] Use CocoaPods & auto-linking on macOS

* [docs] Update setup for macOS

* [package] Include apple dir in distribution

* fix(WKWebview): [iOS] Add shared process pool so cookies and localStorage are shared across webviews (#68)

* Add optional shared process pool

BREAKING CHANGE: useSharedProcessPool prop is set to true by default. If you want the old behavior, please use useSharedProcessPool={false}