Add APIs

- AppRegistry
- AppState
- AsyncStorage
- Dimensions
- NativeMethods
- NetInfo
- PixelRatio
- Platform
- UIManager

docs/apis/AppState.md

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+## AppState
+
+`AppState` can tell you if the app is in the foreground or background, and
+notify you when the state changes.
+
+States
+
+* `active` - The app is running in the foreground
+* `background` - The app is running in the background (i.e., the user has not focused the app's tab).
+
+## Properties
+
+static **currentState**
+
+Returns the current state of the app: `active` or `background`.
+
+## Methods
+
+static **addEventListener**(type: string, handler: Function)
+
+Add a handler to `AppState` changes by listening to the `change` event type and
+providing the `handler`. The handler is called with the app state value.
+
+static **removeEventListener**(type: string, handler: Function)
+
+Remove a handler by passing the change event `type` and the `handler`.
+
+## Examples
+
+To see the current state, you can check `AppStateIOS.currentState`, which will
+be kept up-to-date. This example will only ever appear to say "Current state
+is: active" because the app is only visible to the user when in the `active`
+state, and the null state will happen only momentarily.
+
+```js
+class Example extends React.Component {
+  constructor(props) {
+    super(props)
+    this.state = { currentAppState: AppState.currentState }
+    this._handleAppStateChange = this._handleAppStateChange.bind(this)
+  }
+
+  componentDidMount() {
+    AppState.addEventListener('change', this._handleAppStateChange);
+  }
+
+  componentWillUnmount() {
+    AppState.removeEventListener('change', this._handleAppStateChange);
+  }
+
+  _handleAppStateChange(currentAppState) {
+    this.setState({ currentAppState });
+  }
+
+  render() {
+    return (
+      <Text>Current state is: {this.state.currentAppState}</Text>
+    )
+  }
+}
+```