Docs: add English language support (#170)

* feat: support lang entry build

* feat: vant support lang switch

* move lang iframe-router to utils & fix router link bug

* add en-US config && add some translation

* chang async. to async_ (support superman cdn)

* add layout translation

* change nav style

* upgrade zan-doc

* fix: doc config

* upgrade zan-doc && remove useless code

* fix changelog generate path

docs/examples-docs/zh-CN/progress.md

@@ -0,0 +1,64 @@
+<style>
+.demo-progress {
+  .van-progress {
+    margin: 20px 10px;
+  }
+} 
+</style>
+
+## Progress 进度条
+
+### 使用指南
+``` javascript
+import { Progress } from 'vant';
+
+Vue.component(Progress.name, Progress);
+```
+
+### 代码演示
+
+#### 基础用法
+
+进度条默认为蓝色，使用`percentage`属性来设置当前进度
+
+:::demo 基础用法
+```html
+<van-progress :percentage="0"></van-progress>
+<van-progress :percentage="46"></van-progress>
+<van-progress :percentage="100"></van-progress>
+```
+:::
+
+
+#### 进度条置灰
+
+:::demo 进度条置灰
+```html
+<van-progress inactive :percentage="0"></van-progress>
+<van-progress inactive :percentage="46"></van-progress>
+<van-progress inactive :percentage="100"></van-progress>
+```
+:::
+
+
+#### 样式定制
+
+可以使用`pivot-text`属性自定义文字，`color`属性自定义进度条颜色
+
+:::demo 样式定制
+```html
+<van-progress pivot-text="红色" color="#ed5050" :percentage="26"></van-progress>
+<van-progress pivot-text="橙色" color="#f60" :percentage="46"></van-progress>
+<van-progress pivot-text="黄色" color="#f09000" :percentage="66"></van-progress>
+```
+:::
+
+### API
+
+| 参数       | 说明      | 类型       | 默认值       | 可选值       |
+|-----------|-----------|-----------|-------------|-------------|
+| inactive | 是否置灰 | `Boolean` | `false` | |
+| percentage | 进度百分比 | `Number` | `false` | `0-100` |
+| pivotText | 文字显示 | `String` | 百分比文字 | - |
+| color | 进度条颜色 | `String` | `#38f` | hexvalue |
+| textColor | 进度条文字颜色 | `String` | `#fff` | hexvalue |