[Improvement] SubmitBar: add left slot (#345)

* 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

* [bugfix] Search box-sizing wrong

* [Doc] update vant-demo respo

* [Doc] translate theme & demo pages

* [Doc] add Internationalization document

* [bugfix] remove unnecessary props

* [fix] optimize clickoutside

* [new feature] optimize find-parent

* [new feature]: change document title accordinng to language

* [new feature] Pagination code review

* [improvement] adjust icon-font unicode

* [improvement] Icon spinner color inherit

* [improvement] icon default width

* [bugfix] DateTimePicker validate date props

* [bugfix] Tab item text ellipsis

* [improvement] optimize single line ellipsis

* [Improvement] optimzie staticClass

* [Improvement] Button: use sfc instread of jsx

* [Improvement] update actionsheet close icon style

* fix: yarn.lock

* fix: icon test cases

* [bugfix] errors during ssr

* [Improvement] SubmitBar add left slot

docs/markdown/en-US/submit-bar.md

@@ -71,7 +71,7 @@ Vue.component(SubmitBar.name, SubmitBar);
 ```
 
 #### Advanced Usage
-提示文案中的额外操作和说明
+通过 slot 插入自定义内容
 
 ```html
 <van-submit-bar
@@ -79,6 +79,7 @@ Vue.component(SubmitBar.name, SubmitBar);
   buttonText="提交订单"
   @submit="onClickButton"
 >
+  <van-checkbox v-model="checked">全选</van-checkbox>
   <span slot="tip">
     您的收货地址不支持同城送, <span @click="onClickEditAddress">修改地址 ></span>
   </span>
@@ -106,4 +107,5 @@ Vue.component(SubmitBar.name, SubmitBar);
 
 | Name | Description |
 |-----------|-----------|
+| default | 自定义订单栏左侧内容 |
 | tip | 提示文案中的额外操作和说明 |