Support for a Counter-caching API about cachetower

[Turnerj]

Thinking about this a little more, I'd probably go down the path of splitting cache layers into categories like:

• Common (This is what already exists)
• Counters (This is what this issue proposes)
• ... (Anything else that may come up later)

Rather than try and squish everything into a single stack and provider, basically have interfaces and providers for each specific "category". Its not like DB or Disk caching would be a high priority for counters but are of reasonable importance for "common" caching.

[Turnerj]

This is still conceptually interesting but deviates from the main goal of the library too much in my opinion, making it harder to maintain the library in the future.