Sidekiq 3.0 support
pass redis_pool argument to support sidekiq v3.0
actually pass redis_pool
add specs for redis_pool
use double instead of OpenStruct
add redis_pool argument rdoc description
add 'expiration' arg description, mark optional args as optional
rename pool arg to redis_pool
Merge remote-tracking branch 'sidekiq-v3/master' for Sidekiq V3 support