[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/stepper.md

@@ -0,0 +1,64 @@
+## Stepper
+
+### Install
+``` javascript
+import { Stepper } from 'vant';
+
+Vue.component(Stepper.name, Stepper);
+```
+
+### Usage
+
+#### Basic Usage
+
+```html
+<van-stepper v-model="value" />
+```
+
+```javascript
+export default {
+  data() {
+    return {
+      value: 1
+    }
+  }
+}
+```
+
+#### Disabled
+
+```html
+<van-stepper v-model="value" disabled />
+```
+
+#### Advanced Usage
+
+```html
+<van-stepper
+  v-model="value"
+  min="5"
+  max="40"
+  step="2"
+  defaultValue="9"
+/>
+```
+
+### API
+
+| Attribute | Description | Type | Default | Accepted Values |
+|-----------|-----------|-----------|-------------|-------------|
+| min | Min value | `String | Number` | `1` | - |
+| max | Max value | `String | Number` | - | - |
+| defaultValue | Default value | `String | Number` | `1` | - |
+| step | Value change step | `String | Number` | `1` | - |
+| disabled | Disable value change | `Boolean` | `false` | - | 
+| disableInput | Disable input | `Boolean` | `false` | - |
+
+### Event
+
+| Event | Description | Arguments |
+|-----------|-----------|-----------|
+| change | Triggered when value change | value: current value |
+| overlimit | Triggered when click disabled button | - |
+| plus | Triggered when click plus button | - |
+| minus | Triggered when click minus button | - |