These new utilities make it easier to test HTTP requests and responses

dealing with multiple paths, and simple responses payloads or errors

with custom headers. It does this through a make_handler_for_paths()

function that takes in a dictionary of information and returns a method

to pass to setup_http_test().
It also adds a dump_json() method that wraps json.dumps() and

returns a bytestring, helping deal with Python 2/3 compatibility.

Used these new methods in upcoming unit tests, which pass.