Configure S3-based deployments via s3cmd

This completes part of the infrastructure requirements for implementing automated website deployments via travis as discussed in #237.

This PR contains all commands necessary to create the bucket, setup the website configuration, set the bucket policy (ensuring that all files will be world-readable) and perform the first deploy. You can run this via: `rake s3:setup`. Subsequent deploys can be run vai `rake s3:deploy`. You will need 3 environment variables set:

- S3_ACCESS_KEY_ID
- S3_SECRET_ACCESS_KEY
- BUCKET_URL

The `BUCKET_URL` must be in the form of s3://{BUCKET_NAME}.

To run the initial setup commands you must have the latest alpha of s3cmd installed (on a Mac via Homebrew `brew install --dev s3cmd`). For other platforms, make sure you install at least 1.5.0-alpha3.

To run the deploys via Travis, we should be able to add:

```
install:
  - sudo apt-get install s3cmd
```

to our .travis.yml and get access to s3cmd that way.

I tested all of this (minus travis integration) using my own S3 account, you can see the site running at http://emberjs.joefiorini.com/.