Update IMAGEKIT_DEFAULT_FILE_STORAGE description
Add __getstate__ method to ImageCacheFile
Merge pull request #255 from nex2hex/develop

Add __getstate__ method to ImageCacheFile
Bump the version to 3.0.4.
Merge branch 'release/3.0.4' into develop

* release/3.0.4:
  Bump the version to 3.0.4.
Added RQ-based async cache file backend
Cache file backends: dropped the "Async" in class names
Merge pull request #258 from mkai/_rq_async_cachefile_backend

Added RQ-based async cache file backend
Fix celery backend
Correct reference to generateimage tag

Closes GH-261