Cache pruning API

[guybedford]

It would be useful to have a cache pruning API that is more than just a global clear cache.

A pruning API might remove based on some rules:

• Remove all cached requests that haven't been accessed for X amount of time
• Remove cached requests from the most stale to reduce the cache size down to X MB

Perhaps these are clearCache arguments:

clearCache({ maxAccessTime: 400 }); // seconds

clearCache({ maxSize: 500 }); // MB