Store holiday list in redis
Remove expired holidays
Add method to clear previous holidays
Use the HolidayCache key constant in specs
Add HolidayCache#retrieve method
Use zremrangebyscore instead of multiple zrems
Change clear to everything

Also json encoding the sorted results set. Not sure why this is
necessary, but doing it for now.
Small specs clean up
Merge pull request #2 from bhicks/populate-redis

Populate redis