[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/layout.md

@@ -0,0 +1,66 @@
+## Layout
+
+Quickly and easily create layouts with `van-row` and `van-col`
+
+### Install
+``` javascript
+import { Row, Col } from 'vant';
+
+Vue.component(Row.name, Row);
+Vue.component(Col.name, Col);
+```
+
+### Usage
+
+#### Basic Usage
+
+Layout are based on 24-column. The attribute `span` in `Col` means the number of column the grid spans. Of course, You can use `offset` attribute to set number of spacing on the left side of the grid.
+
+
+```html
+<van-row>
+  <van-col span="8">span: 8</van-col>
+  <van-col span="8">span: 8</van-col>
+  <van-col span="8">span: 8</van-col>
+</van-row>
+
+<van-row>
+  <van-col span="4">span: 4</van-col>
+  <van-col span="10" offset="4">offset: 4, span: 10</van-col>
+  <van-col span="6">span: 6</van-col>
+</van-row>
+
+<van-row>
+  <van-col offset="12" span="12">offset: 12, span: 12</van-col>
+</van-row>
+```
+
+
+#### Column Spacing
+
+Set grid spacing using `gutter` attribute. The default value is 0
+
+
+```html
+<van-row gutter="20">
+  <van-col span="8">span: 8</van-col>
+  <van-col span="8">span: 8</van-col>
+  <van-col span="8">span: 8</van-col>
+</van-row>
+```
+
+
+### API
+
+#### Row
+| Attribute | Description | Type | Default | Accepted Values |
+|-----------|-----------|-----------|-------------|-------------|
+| gutter | grid spacing（px） | `String | Number` | - | - |
+| prefix | className prefix | `String` | `van` | - |
+
+#### Column
+| Attribute | Description | Type | Default | Accepted Values |
+|-----------|-----------|-----------|-------------|-------------|
+| span | number of column the grid spans | `String | Number` | - | - |
+| offset | number of spacing on the left side of the grid | `String | Number` | - | - |
+| prefix | className prefix | `String` | `van` | - |