[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/icon.md

@@ -0,0 +1,23 @@
+## Icon
+
+### Install
+``` javascript
+import { Icon } from 'vant';
+
+Vue.component(Icon.name, Icon);
+```
+
+### Usage
+
+#### Basic Usage
+View all usable icons on the right.
+
+```html
+<van-icon name="success" />
+```
+
+### API
+
+| Attribute | Description | Type | Default | Accepted Values |
+|-----------|-----------|-----------|-------------|-------------|
+| name | Icon name | `String` | `''` | - |