Retry request on OutOfMemoryError.

Rely on the underlying disk cache to hopefully prevent hitting the network twice.
Merge pull request #58 from square/jw/oom-retry

Retry request on OutOfMemoryError.
Checkstyle fixes.
Use Uri to handle resources loading.

It kills resourceId param and field everywhere.
Add support for loading images from assets

Images can be loaded from assets using a special type of Uri (e.g.
"picasso.assets:/image.png")