拓展 element-ui 组件库 ElMessage 功能，参考https://juejin.cn/post/6844903968309526536

<table>
  <thead>
    <tr>
      <th>Config</th>
      <th>Description</th>
      <th>Default</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>max</td>
      <td>最大显示数量，默认为0，不限制显示数量</td>
      <td>0</td>
    </tr>
    <tr>
      <td>isQueue</td>
      <td>是否以队列形式存储为展示消息</td>
      <td>false</td>
    </tr>
    <tr>
      <td>showNewest</td>
      <td>是否后添加的消息覆盖前面的消息</td>
      <td>true</td>
    </tr>
  </tbody>
</table>

EtMessage example:

```vue
<template>
  <div>
    <el-button @click="open">打开消息提示</el-button>
  </div>
</template>

<script>
import EtMessage from '@/EtMessage/index'

export default {
  mounted() {
    EtMessage.setConfig({ max: 3, isQueue: false, showNewest: true })
  },

  methods: {
    open() {
      EtMessage.success(`这是一条消息提示 ${new Date()}`)
    },
  },
}
</script>
```