adjust riak VM spec
Add Server-Side encryption option to S3

Adds an attribute that can be used with S3 storage to enable Server-Side
encryption for files uploaded to S3. This is done by include the header
`x-amz-server-side-encryption` as outlined in the Amazon S3 SDK:

http://docs.aws.amazon.com/AmazonS3/latest/dev/UsingServerSideEncryption.html

Related Issue: #408
Add support for S3 `storage_class`

This commit adds support for the S3 `storage_class` header to allow for
objects uploaded to be stored with the `REDUCED_REDUNDANCY` flag. This
defaults to `:standard`, which does not send a special header to the AWS
API.

http://docs.aws.amazon.com/AmazonS3/latest/dev/SetStoClsOfObjUploaded.html
add VM spec; refactor
Storage::S3 server-side encryption and reduced redundancy support

closes #438, closes #408
update installation instructions
Release v3.5.0