[new feature] add Tabbar component (#204)

* [Document] add english document of Checkbox

* [Document] add english document of Field

* [Document] add english document of NumberKeyboard

* [bugfix] NumberKeyboard should not dispaly title when title is empty

* [Document] add english document of PasswordInput

* [Document] add english document of Radio

* [document] add english document of Switch

* [bugfix] remove redundent styles in english document

* [Document] fix details

* fix Switch test cases

* [bugfix] Swipe shouid reinitialize when item changes

* [new feature] ImagePreview reconstruct

* [new feature] add Tabbar component

packages/index.js

@@ -50,6 +50,8 @@ import SwipeItem from './swipe-item';
 import Switch from './switch';
 import SwitchCell from './switch-cell';
 import Tab from './tab';
+import Tabbar from './tabbar';
+import TabbarItem from './tabbar-item';
 import Tabs from './tabs';
 import Tag from './tag';
 import Toast from './toast';
@@ -108,6 +110,8 @@ const components = [
   Switch,
   SwitchCell,
   Tab,
+  Tabbar,
+  TabbarItem,
   Tabs,
   Tag,
   TreeSelect,
@@ -182,6 +186,8 @@ export {
   Switch,
   SwitchCell,
   Tab,
+  Tabbar,
+  TabbarItem,
   Tabs,
   Tag,
   Toast,