Rpqueue

[added] the ability to add items to data queues in the future; see:
`Data.put_data(..., delay=...)`. Works similarly to how delayed tasks
work.

[added] the ability for callers to call stubs instead of needing to have all of
your task / caller code in the same repository. See:
`rpqueue.call_task(name, None or override_queue, *args, **kw)` and
`rpqueue.known_tasks[name].execute(*args, **kwargs)`

[fixed] the in some cases, rpqueue could return 'done' for a task status when it
was actually 'started'. Thanks to github user https://github.com/posix4e for
the bug report. Also noticed that there is an 'unknown' case where we can be
in one of 2 states, but we'll go ahead and call that 'done' as well.

[fixed] periodic tasks should now work. Sorry about that :/

[fixed] issues with cron tasks and periodic tasks, releasing 0.31.0 because
0.30.* is apparently cursed

[fixed] issue with redis-py <2.* connections