Support for Redis Sentinel
Support Sentinel in initialization
Fix JSON typo
Replace implementation of SentinelConnectionPool

- Create a Gevent-friendly, blocking, Sentinel connection pool.
- Other misc. fixes.
Documentation and style updates
Merge pull request #4 from tellapart/devel-sentinel

Change Taba Server to use Redis Sentinel

- Change the base Redis engine to assume connections are managed by Sentinel processes, instead of connecting directly to the master instance.
- Add new implementation of a Sentinel-enabled, blocking, gevent-friendly connection pool.
- Add some new-style example settings files.
- Misc. fixes.