Add Card Reader API support for Full Contact

This commit adds basic support for the Card Reader API http://www.fullcontact.com/developer/docs/card-reader/, specifically the View Requests method.

I have tested only the page parameter but the other parameters (returnedData, format, and diagnostics) should also be supported, although for the format parameter, it doesn't make sense to return XML as the existing gem expects JSON.

The Readme.md has been updated with sample usage.