remove trailing whitespace. [ci skip]
configure `extra_attributes` for `Rack::FakeCAS`.

This patch allows you to configure `extra_attributes` for testing.
The configuration is passed when instantiating the `Rack::FakeCAS` middleware:

    use Rack::FakeCAS, {}, {"jane" => {"name" => "Jane Doe"}}

The Hash has the following structure:

    {<username> => <extra attributes Hash>}

As Rails users most likely do not configure `Rack::FakeCAS` themselves they can
pass the configuration throuth `Rails.application.config`:

    config.rack_cas.fake_attributes = {"jane" => {"name" => "Jane Doe"}}
Merge pull request #13 from senny/configure_fake_attributes

Configure extra attributes for `Rack::FakeCAS`