Versioning for 0.2.0

```
## 0.2.0

- Support for Chrome extension APIs was added.  You should now import one of the
following libraries, as appropriate:
	- Packaged apps: `import 'package:chrome/app.dart';`
	- Extensions: `import 'package:chrome/ext.dart';`
- Work on the `chrome.app.window` API including several breaking changes, please
refer to the dartdoc for usage.
- Added identity support and example
```