added typescript declarations

Author: Kalle Ott

index.d.ts

@@ -0,0 +1,18 @@
+import { NativeModules, ToastAndroid, Platform } from 'react-native'
+
+declare var SimpleToast: {
+  // Toast duration constants
+  SHORT: number,
+  LONG: number,
+
+  // Toast gravity constants
+  TOP: number,
+  BOTTOM: number,
+  CENTER: number,
+
+  show: (message: string, duration: number) => void,
+
+  showWithGravity: (message: string, duration: number, gravity: number) => void
+}
+
+export default SimpleToast