Added feature to disable success_action_redirect and use success_action_status instead

The motivation for this feature was to make carrierwave_direct compatible with jquery-fileupload.
I've added the ```config.use_action_status ``` to enable the replacement of ```success_action_redirect ``` with ```success_action_status ``` in the form sent to s3.  The value of ```config.use_action_status ``` also defaults to false in order preserve original carrierwave_direct behavior.

To use the feature set ```config.use_action_status = true ``` in the carrierwave initializer, and set ```your_uploader.success_action_status = "200" ```or another status (s3 defaults to 204).

Then when creating the form use ```f.file_field :avatar, use_action_status: true ``` to make sure the form matches the new policy.


Also, I'm currently using carrierwave_direct in a project thats going to hit production soon, so I would be interesting in becoming a maintainer!  I'd like to resolve some of the open issues and maybe add a few more features in the future (such as support for multiple uploaders in the same form).

Also, on a side note: I've set up carrierwave_direct to work with s3 in production and localhost for development, and I would be able to write up a how to if your interested.