Page Cache to Stash Cache

[joe-meyer]

I feel there could be some major benefits to moving the page cache to the stash library. There was small discussion on pr #2492

There was some argument that varnish might not be a great fit into the model of stash, but I think it would be fairly trivial to implement a varnish driver which checks to makes sure it's acting on Collection objects. If it isn't, that's fine it just doesn't save to varnish cache, and if it does, it can easily act on the cache appropriately when the cache object is added / removed.

By leveraging stash we not only allow for the flexibility of additional drivers, but also driver pools and tiered caching levels (not to mention we'd already have numerous caching drivers available to us then to use).

[joe-meyer]

Work in progress at #2829

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions!