Fix bug where the drawable callback would return the cached drawable (which may be the default drawable).
This is not ideal. The callback should only return a drawable if the drawable was successfully loaded from an Url.
If it was not loaded from an url, it should call back with null.
Also Fix bug where downloaded cache policy was potentially not being respected.
Add comments to how the UrlImageViewCallback works.
fix bug where callback is not invoked when load fails.
more comments about callbacks
Comment out potentially erroneous assert?
Assert that setUrlDrawable is only called from the main thread.
All accesses to the hashmaps are done on the main thread to prevent locking issues. Not to mention that UI operations must be on the main thread anyways.
fix nre on getImmediateMutableDrawable. need to rename this function to something not stupid,
Major refactor:
Instead of caching Drawables, cache the actual bitmaps themselves.
This was necessary, because Drawables are mutated via their corresponding ImageViews
via setBounds etc.
For example, if an ImageView scales a drawable down, this has the effect of scaling
the drawawble down for all other ImageViews using the same drawable.
By caching bitmaps, and refcounting using the finalizer, unique Bitmap/ZombieDrawable
instances can be used. Under the hood, the Bitmap is still cached and used
by multiple Drawables.

There were also breaking API changes (regarding loaders and callbacks) that could not
be avoided without gimping the API.
Change getBitmap to the more accurate description getCachedBitmap.
prevent redundant ZombieDrawable allocation
ZombieDrawable info
post refactor fixups around bitmap caching and callbacks
Take the max age of a file in account. #51
Dont use junit.framework.Assert#assert. User assert() instead.
Dont use junit.framework.Assert#assert. User assert() instead.
Merge pull request #55 from ChristianBecker/noUnitAsserts

Dont use junit.framework.Assert#assert. Use assert() instead.
Merge pull request #54 from ChristianBecker/master

cleanup: Take the age parameter in account
Update README.md
Revert "Update README.md"

This reverts commit 7e8754dc8675ccdfdbc8d3e95c492c927e866f0e.
Update README.md