Sorted list insertion and deletion script [WIP]

This is just to stage what I have right now.

[Sorted list](http://redis.io/topics/data-types#sorted-sets) is relevant to issues #162 and #158. This script makes it easy to maintain the list of featured games (sorted by rank) and the list of pending game queue.

Todo:
- [x] add deletion script
- ~~call the scripts through [redis.eval](http://redis.io/commands/EVAL)~~ To be completed in #181