Resume Recommendations Request/Response

This change is to add resume recommendations to the external api wrapper.
In order to test, copy and paste the code below into terminal (replacing dev key with real one)..........

bundle
bundle exec pry
require 'Cb'

Cb.configure do |config|
  config.dev_key = 'place_dev_key_here'
  config.time_out = 30
  config.debug_api = true
end

client = Cb::Client.new
request = Cb::Requests::Recommendations::Resume.new({:resume_hash => '9b13d2082bfeb71d36d109ae300f066adaea64e6770ec055252f1c0dfb3eee09', :external_user_id => 'XRHN41N711FXMCP6CVQD'})

client.execute(request)
Prefer expect over should: `expect(request.http_method).to eq :get`
Same in your test names, too - don't use "should" and just say what it *does*.
Also, there are two tests in this one test block. 

``` ruby
it { expect(request.endpoint_uri).to eq Cb.configuration.uri_recommendation_for_resume.sub(':resume_hash', '') }
it { expect(request.http_method).to eq :get }
```