Show download progress imageview like instagram's loading imageView
###How to use
Just instance a RoundProgressImageView example as roundImageView and then
[roundImageView prSetImageWithURL:imageURL placeholderImage:nil];
###Goodness
- Support cancel the image load.
- If the image load failed, support tapping to reload the image.
###Demo
- Feed shows how to show images like instagram
- Some tricky to load batch images and catch background
###Credits
This is build base on SDWebImage.