Fixes invalidating image within cache when image is nil.
Renames and improves added test.
Merge pull request #42 from julianhirt/FixesResettingImageForKey

Fixes invalidating image within cache when image is nil.
Merge pull request #43 from blushmessenger/master

removeAllImages doesn't rebuild disk cache
Add unit test for bug #43
Remove disk cache contents one by one instead of removing and recreating the directory
Increase version
When saving to disk, get rep not on main thread
async back to main thread before accessing disk cache
Merge pull request #50 from foursquare/master

Get image data in background