Add a utility method called "get_all_list_data" that will iterate throug...

...h a response object's link headers and returns a list of all the json data.  Added tests and Sphinx documentation blocks.  Update modules in the client package to use relative imports, as it is a best practice.  Import get, put, post, and delete methods in client package __init__.py to make it easier for end user and for methods to call the API.
Were there cases where the canvas_sdk import failed? I seem to remember PEP8 saying that while relative imports were acceptable, absolute imports should be preferred.