Publish to s3 support.

The first time run this command it'll ask you to enter the docs AWS creds. After that you shouldn't have to do it anymore.

Also, this rake task uses s3cmd which you can brew install or follow the link in the error output. That tool seems to beat any ruby library out currently to accomplish this task.
Revert version bump and will do that on master
Restart vault-docs for users of heroku go CLI 'hk' may change, but I'll change it.
Merge pull request #40 from heroku/doc_publish

Publish to s3 support.