Add Amazon S3 deploy option to rake tasks

- Use Rakefile config for bucket name
- Use `ENV['AWS_ACCESS_KEY_ID']` and `ENV['AWS_SECRET_ACCESS_KEY']` for credentials
- Assumes you have completed the [official web hosting setup](http://docs.aws.amazon.com/AmazonS3/latest/dev/WebsiteHosting.html)
Add s3_init rake task

This will create the S3 bucket, enable static website hosting, and
configure a policy which allows read access to all objects
Merge branch 's3-deploy' of https://github.com/kolorahl/octopress into 2.1
Initial check in.