This is a simple Sinatra application which demonstrates how to upload
files directly to Amazon S3. As S3 does not allow more than one file to
be uploaded per request, the application uses the jQuery form plugin to
handle uploading multiple files.

To use the application you must create a config.yml file which defines
the following keys:

  :access_key_id      => AWS access key id
  :secret_access_key  => AWS secret access key
  :bucket             => S3 bucket to upload to
  :redirect_url       => URL to redirect to after successful upload
  :max_file_size      => Largest file size (in bytes) S3 should accept

The config.yml settings can be defined at the top-level or they can be
namespaced under the name of the runtime environment much like the
database.yml file in a Rails project.

TODO

* Gracefully handle upload failures (parse S3's XML response)
* Minimal progress indicator, e.g., say "Uploading..."