[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/pull-refresh.md

@@ -0,0 +1,66 @@
+## PullRefresh
+
+### Install
+``` javascript
+import { PullRefresh } from 'vant';
+
+Vue.component(PullRefresh.name, PullRefresh);
+```
+
+### Usage
+
+```html
+<!-- use v-model to control loading status -->
+<van-pull-refresh
+  v-model="isLoading"
+  pulling-text="Pull to refresh..."
+  loosing-text="Loose to refresh..."
+  loading-text="Loading..."
+>
+  <p>Refresh Count: {{ count }}</p>
+</van-pull-refresh>
+```
+
+```javascript
+export default {
+  data() {
+    return {
+      count: 0,
+      isLoading: false
+    }
+  },
+
+  watch: {
+    isLoading() {
+      if (this.isLoading) {
+        setTimeout(() => {
+          Toast('Refresh Success');
+          this.isLoading = false;
+          this.count++;
+        }, 500);
+      }
+    }
+  }
+}
+```
+
+### API
+
+| Attribute | Description | Type | Default | Accepted Values |
+|-----------|-----------|-----------|-------------|-------------|
+| v-model | Loading status | `Boolean` | - | - |
+| pullingText | Text to show when pulling | `String` | `下拉即可刷新...` | - |
+| loosingText | Text to show when loosing | `String` | `释放即可刷新...` | - |
+| loadingText | Text to show when loading | `String` | `加载中...` | - |
+| animationDuration | Animation duration | `Number` | `300` | - |
+| headHeight | Height of head | `Number` | `50` | - |
+
+### Slot
+
+| name | Description |
+|-----------|-----------|
+| - | Default slot |
+| normal | Content of head when at normal status |
+| pulling | Content of head when at pulling |
+| loosing | Content of head when at loosing |
+| loading | Content of head when at loading |