Dalli integration

[saiqulhaq]

on the readme, it says we have to use memcached_store. however I found that Dalli also has CAS support. what should we do to make Dalli can work with Identity Cache gem?

[dylanahsmith]

It doesn't look like active support's ActiveSupport::Cache::MemCacheStore provides CAS support or exposes the underlying Dalli::Client instance, so I think we need to add CAS support to active support if we want to integrate with ActiveSupport::Cache::MemCacheStore.

Alternatively, we can provide a cache adapter that integrates with a Dalli::Client instance directly. The cache adapter will be used by IdentityCache::CacheFetcher if it provides cas and cas_multi methods that behave like those provided by the memcached_store gem. In addition to those methods, it will also need to provide a write method that behaves like ActiveSupport::Cache::Store.

[saiqulhaq]

#465