Django-s3sign

==================
* Adjust S3Upload.file_dom_selector to allow for any DOM selector
rather than just an ID.
* Introduced new optional param `file_dom_el` for passing in the file
input element directly. This is convenient when initializing
S3Upload from an event, as you can just pass in the event.target
object.

==================
* Fixed bug where `acl` attribute was not working, preventing the
ability to upload objects with `public-read` access.

==================
* Don't call onProgress event handler if file list is empty.

==================
* Use default max file size of 2gb.
* Update default expiration time to 8 hours.
* Introduce configurable region name, via
`AWS_S3_REGION_NAME`. Defaults to us-east-1.

==================
* Use presigned POST request instead of PUT.
* Add a configurable policy limit (default 4mb) for uploads.

==================
* Move s3 signing functions out of the view so they can be imported
and used separately.
* Add bmp image support.