上传图片
## onion.upload
### 功能
用于图片上传
### 使用场景
表单中需要上传图片时
### 如何使用
**onion.upload(options, callback)**
options 为 [自定义属性](https://www.layui.com/doc/modules/upload.html), callback 为回调
### api定义
``` javascript
onion.upload = function (options, callback) {
var defaultOpts = {
elem: '',
url: '',
data: {},
accept: 'images',
acceptMime: 'image/*',
done: function () {
var args = arguments;
callback && callback(args);
},
error: function () {
var args = arguments;
callback && callback(args);
}
}
var currentOpts = $.extend({}, defaultOpts, options || {});
currentOpts.url = onion.onionUrl + currentOpts.url;
return upload.render(currentOpts)
}
```