#366 Initial Commit of Atlas ATS API

This is an initial commit of my work on the Atlas ATS API for XChange.  I've run into several snags with regards to API changes and some difficulty with the reference documentation on apiary.io not entirely matching the ruby reference implementation here on Github.  I've been utilizing Unit and Integration Testing throughout to verify my code's functionality.  There is an issue that the test API is not unified properly so that certain unit and integration tests break depending on which url endpoints are used for testing.