In lib.api_callers, get_responses accepts only a fully formed API call URL, with the params in the string.

But, request.get (the underlying method within BasePagedResponseGetter), accepts a dictionary of parameters. Instead of requiring the user to form the full URL first, we could accept an optional dictionary of parameters to pass down to request.get.

(Moved from crickets-and-comb/bfb_delivery#61 after api_callers moved over.)