Add offline maps js module

src/Offline.js

+import {NativeModules, NativeEventEmitter} from 'react-native'
+const {AMapOffline} = NativeModules
+
+export default {
+  getProvinces: () => AMapOffline.getProvinces(),
+  getCities: () => AMapOffline.getCities(),
+  download: name => AMapOffline.getDownload(name),
+}

src/index.js

@@ -6,7 +6,8 @@ import Circle from './maps/Circle'
 import HeatMap from './maps/HeatMap'
 import MultiPoint from './maps/MultiPoint'
 import Navigation from './navigation'
-import MapUtils from './Utils'
+import Utils from './Utils'
+import Offline from './Offline'
 
 MapView.Marker = Marker
 MapView.Polyline = Polyline
@@ -25,5 +26,6 @@ export {
   HeatMap,
   MultiPoint,
   Navigation,
-  MapUtils,
+  Utils,
+  Offline
 }