Adding state data list

To test this locally:

bundle
bundle exec irb
require 'Cb'
require 'pry'

Cb.configure do |config|
  config.dev_key    = 'GetYourOwnDevKey'
  config.time_out  = 30
  config.debug_api  = true
end

input = {country_code: 'US'}
client = Cb::Client.new
request = Cb::Requests::State::Get.new(input)
response = client.execute(request)
An assertion on the `value` property would be good here, as it would at least showcase/document-through-testing the other half of this object's public API.