Gem doesn't work as described

Hi Ben,

Thanks for making this gem.

However, I can't get the gem to work as you describe in the readme.

I try running the following code:

``` ruby
require "rubygems"
require "amazon-associates"

Amazon::Ecs.options = {:aws_access_key_id => "123"}
```

But get the following error:

``` ruby
NameError: uninitialized constant Amazon::Ecs
```

Hope you can help.

Thanks in advance,
/Lasse
