Server-side encryption option and clean up temp folder

To make this module more secure, I added a couple features to my fork.
1. Clean up tmp folders after s3 upload or error
2. Add an option to use AWS server-side-encryption. All that's required is [adding a simple header to the put](http://docs.aws.amazon.com/AmazonS3/latest/dev/SSEUsingRESTAPI.html)

Tested both of these locally and they seem to work swimmingly