[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/popup.md

@@ -0,0 +1,48 @@
+## Popup
+
+### Install
+``` javascript
+import { Popup } from 'vant';
+
+Vue.component(Popup.name, Popup);
+```
+
+### Usage
+
+#### Basic Usage
+Popup is located in the middle of the screen by default
+
+```html
+<van-popup v-model="show">Content</van-popup>
+```
+
+```javascript
+export default {
+  data() {
+    return {
+      show: false
+    }
+  }
+};
+```
+
+#### Position
+Use `position` prop to set popup display position
+
+```html
+<van-popup v-model="show" position="top" :overlay="false">
+  Content
+</van-popup>
+```
+
+### API
+
+| Attribute | Description | Type | Default | Accepted Values |
+|-----------|-----------|-----------|-------------|-------------|
+| v-model | Whether to show popup | `Boolean` | `false` | - |
+| overlay | Whether to show overlay | `Boolean` | `true` | - |
+| lockOnScroll | Lock body scroll | `Boolean` | `false` | - |
+| position | Position | `String` | - | `top` `bottom` `right` `left` |
+| closeOnClickOverlay | Close popup when click overlay | `Boolean` | `true` | - |
+| transition | Transition | `String` | `popup-slide` | - |
+| preventScroll | Prevent background scroll | `Boolean` | `false` | - |