[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/loading.md

@@ -0,0 +1,38 @@
+## Loading
+
+### Install
+``` javascript
+import { Loading } from 'vant';
+
+Vue.component(Loading.name, Loading);
+```
+
+### Usage
+
+#### Solid Circle
+
+```html
+<van-loading type="circle" color="black" />
+<van-loading type="circle" color="white" />
+```
+
+#### Gradient Circle
+
+```html
+<van-loading type="gradient-circle" color="black" />
+<van-loading type="gradient-circle" color="white" />
+```
+
+#### Spinner
+
+```html
+<van-loading type="spinner" color="black" />
+<van-loading type="spinner" color="white" />
+```
+
+### API
+
+| Attribute | Description | Type | Default | Accepted Values |
+|-----------|-----------|-----------|-------------|-------------|
+| color | Color | `String` | `black` | `black` `white` |
+| type | Type | `String` | `gradient-circle` | `spinner` `circle` |