Add new function SetSheetBackgroundFromBytes used for setting background image by given image data

[jianxinhou]

Because of business need, I want to add a new method(SetSheetBackgroundFromBytes) for struct File.

the function of this method is similar with existing method(SetSheetBackground), they both can add background image for excel files, but the difference between SetSheetBackground and SetSheetBackgroundFromBytes is, the new method use binary image data as image source. And SetSheetBackgroundFromBytes do not need to specify the extension of image data, It can determine the image format by itself.

由于业务需要，我想为File结构体增加一个新的方法：SetSheetBackgroundFromBytes。

该方法的功能与现存SetSheetBackground方法相同，即添加背景图像，不同的是新增方法支持使用二进制数据设置背景图像，同时，SetSheetBackgroundFromBytes无需指定文件后缀，该方法可自行判断二进制数据中所包含图像的格式。

[xuri]

Thanks for your issue. I'll certainly accept that patch if you did that.

[jianxinhou]

pull-request created!