Requests return a Sift::Response

This release introduces a non-backward-compatible API change for the new_account() and get_accounts() methods. Whereas previously they would return a hash of data on success, and print an error message that was then implicitly returned in case of failure, they now return a Sift::Response object in either case. Callers will need to check for validity with the .ok? method on the response and then get the response body using .body.

Added support for next_ref while getting accounts

Fetching partner accounts now returns a limit of 100 per call. This change allows the caller to pass the next_ref back in to get the next set of results.