[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/nav-bar.md

@@ -0,0 +1,47 @@
+## NavBar
+
+### Install
+``` javascript
+import { NavBar } from 'vant';
+
+Vue.component(NavBar.name, NavBar);
+```
+
+### Usage
+
+#### Basic Usage
+
+```html
+<van-nav-bar
+  title="Title"
+  leftText="Back"
+  rightText="Button"
+  leftArrow
+/>
+```
+
+#### Advanced Usage
+
+```html
+<van-nav-bar title="Title" leftText="Back" leftArrow>
+  <van-icon name="search" slot="right" />
+</van-nav-bar>
+```
+
+
+### API
+| Attribute | Description | Type | Default | Accepted Values |
+|-----------|-----------|-----------|-------------|-------------|
+| title | Title | `String` | `''` | - |
+| leftText | Left Text | `String` | `''` | - |
+| rightText | Right Text | `String` | `''` | - |
+| leftArrow | Whether to show left arrow | `Boolean` | `false` | - |
+| fixed | Whether to fixed top | `Boolean` | `false` | - |
+
+### Slot
+
+| name | Description |
+|-----------|-----------|
+| title | Custom title |
+| left | Custom left side content |
+| right | Custom right side content |