[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/field.md

@@ -0,0 +1,103 @@
+## Field
+
+### Install
+``` javascript
+import { Field } from 'vant';
+
+Vue.component(Field.name, Field);
+```
+
+### Usage
+
+#### Basic Usage
+The value of filed is bound with v-model.
+
+```html
+<van-cell-group>
+  <van-field v-model="value" placeholder="Username"></van-field>
+</van-cell-group>
+```
+
+#### Custom type
+Use `type` prop to custom diffrent type fileds.
+
+```html
+<van-cell-group>
+  <van-field
+    v-model="username"
+    label="Username"
+    icon="clear"
+    placeholder="Username"
+    required
+    @click-icon="username = ''"
+  >
+  </van-field>
+
+  <van-field
+    v-model="password"
+    type="password"
+    label="Password"
+    placeholder="Password"
+    required>
+  </van-field>
+</van-cell-group>
+```
+
+#### Disabled
+
+```html
+<van-cell-group>
+  <van-field value="Disabled" label="Username" disabled></van-field>
+</van-cell-group>
+```
+
+#### Error info
+
+```html
+<van-cell-group>
+  <van-field label="Username" placeholder="Username" error></van-field>
+</van-cell-group>
+```
+
+#### Auto resize
+Textarea Filed can be auto resize when has `autosize` prop
+
+```html
+<van-cell-group>
+  <van-field
+    v-model="message"
+    label="Message"
+    type="textarea"
+    placeholder="Message"
+    rows="1"
+    autosize
+  >
+  </van-field>
+</van-cell-group>
+```
+
+### API
+
+| Attribute | Description | Type | Default | Accepted Values |
+|-----------|-----------|-----------|-------------|-------------|
+| type | Filed type | `String` | `text` | `number` `email` <br> `textarea` `tel` <br> `datetime` `date` <br> `password` `url` |
+| value | Filed value | `String` | - | - |
+| label | Filed label | `String` | - | - |
+| disabled | Disable field | `Boolean` | `false` | - |
+| error | Whether to show error info | `Boolean` | `false` | - |
+| autosize | Textarea auto resize | `Boolean` | `false` | - |
+| icon | Right side Icon name | `String` | - | - |
+
+### Event
+
+| Event | Description | Parameters |
+|-----------|-----------|-----------|
+| focus | Triggered when filed get focused | - |
+| blur | Triggered when blur filed | - |
+| click-icon | Triggered when click the icon of filed | - |
+
+### Slot
+
+| name | Description |
+|-----------|-----------|
+| icon | Custom icon |