Redis store implementation

An alternative store which implements all of ActiveRecord store's interface.

To use this Redis store, add/uncomment these in initializers/rapns.rb:

require 'connection_pool'
require 'rapns/daemon/store/redis_store'
Rapns::Notification.send(:include, Rapns::NotificationAsRedisObject)

Rapns.configure do |config|
...
  config.store = :redis_store
  config.redis_host = "localhost"
  config.redis_port = 6379
  config.number_of_connections = 5
  config.connection_timeout = 1
  config.stalled_notification_tolerence = 3600
...
end

To save a notification for sending:
notification.save_to_redis