[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/button.md

@@ -0,0 +1,77 @@
+## Button
+
+### Install
+``` javascript
+import { Button } from 'vant';
+
+Vue.component(Button.name, Button);
+```
+
+### Usage
+
+#### Type
+
+```html
+<van-button type="default">Default</van-button>
+<van-button type="primary">Primary</van-button>
+<van-button type="danger">Danger</van-button>
+```
+
+#### Size
+
+```html 
+<van-button size="large">Large</van-button>
+<van-button size="normal">Normal</van-button>
+<van-button size="small">Small</van-button>
+<van-button size="mini">Mini</van-button>
+```
+
+#### Disabled
+
+```html
+<van-button disabled>Diabled</van-button>
+```
+
+#### Loading
+
+```html 
+<van-button loading></van-button>
+<van-button loading type="primary"></van-button>
+```
+
+#### Custom Tag
+Use `tag` prop to custom button tag
+
+```html 
+<van-button tag="a" href="https://www.youzan.com" target="_blank">
+  Button
+</van-button>
+```
+
+#### Action Button
+
+```html 
+<van-button type="primary" bottomAction>Button</van-button>
+
+<van-row>
+  <van-col span="12">
+    <van-button bottomAction>Button</van-button>
+  </van-col>
+  <van-col span="12">
+    <van-button type="primary" bottomAction>Button</van-button>
+  </van-col>
+</van-row>
+```
+
+### API
+
+| Attribute | Description | Type | Default | Accepted Values |
+|-----------|-----------|-----------|-------------|-------------|
+| type | Type | `String` | `default` | `primary` `danger` |
+| size | Size | `String` | `normal` | `large` `small` `mini` |
+| tag | Tag | `String` | `button` | - |
+| nativeType | Native Type Attribute | `String` | `''` | - |
+| diabled | Whether disable button | `Boolean` | `false` | - |
+| loading | Whether show loading status | `Boolean` | `false` | - |
+| block | Whether to set display block | `Boolean` | `false` | - |
+| bottomAction | Whether to be action button | `Boolean` | `false` | - |