Update Rails project to consume new Stormpath SDK

### Updating Rails client to consume new Stormpath SDK.

1. Adding some functional tests (which go all the way to the Stormpath API) to assist in development of the Rails gem. These tests rely on environment variables to obtain their application, directory, API key ID, and API key secret values.

1. Added SimpleCov for code coverage-reporting (dumps to ./coverage/).

1. Removed the install generator and use of YAML completely. Rails client now obtains application and directory URL through ENV. Application and directory must be provisioned (and linked as a "login source") through Stormpath Administration UI before Rails client is operable. Updated README to reflect this change.