Leaderboard

* Fix an edge case in the updated comparison for non-members

* Fix running under Python 3 for `ranked_in_list(...)` if `include_missing` is `True` and non-member(s) passed in

* Fix `around_me_in` for Python 3+ [49](https://github.com/agoragames/leaderboard-python/issues/49)
* Fix TieRankingLeaderboard init [47](https://github.com/agoragames/leaderboard-python/pull/51)

* Fixed an error with the `ranked_in_list` method when using certain options [46](https://github.com/agoragames/leaderboard-python/pull/46)
* Added `total_scores` method [45](https://github.com/agoragames/leaderboard-python/pull/45)

* Remove `izip_longest` import where unneeded. [44](https://github.com/agoragames/leaderboard-python/pull/44)

* More pipelining as per Ruby library, [58](https://github.com/agoragames/leaderboard/pull/58).
Also adds `members_data_for(...) and `members_data_for_in(...)` methods.
* Guard against an out of bounds index in `member_at`