[new feature] add i18n support (#310)

* fix: Tabbar icon line-height

* [new feature] progress add showPivot prop

* [new feature] TabItem support vue-router

* [new feature] update document header style

* [Doc] add toast english ducoment

* [new feature] add i18n support

* feat: Extract demos from markdown

* feat: Base components demos

* [new feature] complete demo extract & translate

* [fix] text cases

* fix: add deepAssign test cases

* fix: changelog detail

* [new feature] AddressEdit support i18n

docs/markdown/en-US/quickstart.md

@@ -0,0 +1,60 @@
+## Vant
+
+Mobile UI Component based on `Vue 2.0`
+
+### Install
+
+```shell
+npm i vant -S
+```
+
+### Usage
+
+#### 1. Use [babel-plugin-import](https://github.com/ant-design/babel-plugin-import) (Recommended)
+```bash
+# Install babel-plugin-import
+npm i babel-plugin-import -D
+```
+
+```js
+// set babel config in .babelrc or babel-loader
+{
+  "plugins": [
+    ["import", { "libraryName": "vant", "style": true }]
+  ]
+}
+```
+
+Then you can import components from vant, equivalent to import manually below.
+
+```js
+import { Button } from 'vant';
+```
+
+#### 2. Manually import
+
+```js
+import { Button } from 'vant/lib/button';
+import 'vant/lib/vant-css/base.css';
+import 'vant/lib/vant-css/button.css';
+```
+ 
+#### 3. Import all components
+
+```js
+import Vue from 'vue';
+import Vant from 'vant';
+import 'vant/lib/vant-css/index.css';
+
+Vue.use(Vant);
+```
+
+### CDN
+
+```html
+<!-- import style -->
+<link rel="stylesheet" href="https://unpkg.com/vant/lib/vant-css/index.css" />
+
+<!-- import script --><script></script>
+<script src="https://unpkg.com/vant/lib/vant.min.js"></script>
+```