converted blog into module

Hi netyum,

thanks for you great work!
I'd be pleased if you merge this, but this first and foremost a message to you.

I converted your app into a standalone blog module with migrations, see the [README](https://github.com/schmunk42/yii2-blog/blob/master/README.md) for details. I will add this as a first reference in the discussion of this [issue](https://github.com/yiisoft/yii2/issues/389).

Let me know if you have questions.


Best regards,
schmunk