Update README with examples of pure Dart JSONP

This library isn't really required anymore.
Remove releaseData

No longer required, when the objects are now eligible for garbage
collection in the normal way.
Remove old js library, and js.Proxy type
Update example imports
Fix json handlers in example
Update references to return type

The return type is still wrapped (a JsObject) but it can be treated
like a dictionary without issue.
Reapply styles

Allowing styles to flow into the shadow dom no longer works.
Increase version
Merge branch 'release/1.0.1' into develop