[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/panel.md

@@ -0,0 +1,47 @@
+## Panel
+
+### Install
+``` javascript
+import { Panel } from 'vant';
+
+Vue.component(Panel.name, Panel);
+```
+
+### Usage
+
+#### Basic Usage
+
+```html
+<van-panel title="Title" desc="Description" status="Status">
+  <div>Content</div>
+</van-panel>
+```
+
+#### Advanced Usage
+
+```html
+<van-panel title="Title" desc="Description" status="Status">
+  <div>Content</div>
+  <div slot="footer">
+    <van-button size="small">Button</van-button>
+    <van-button size="small" type="danger">Button</van-button>
+  </div>
+</van-panel>
+```
+
+### API
+
+| Attribute | Description | Type | Default | Accepted Values |
+|-----------|-----------|-----------|-------------|-------------|
+| title | Title | `String` | - | - |
+| desc | Description | `String` | - | - |
+| status | Status | `String` | - | - |
+
+
+### Slot
+
+| name | Description |
+|-----------|-----------|
+| - | Default slot |
+| header | Custom header |
+| footer | Custom footer |