TODO

- test memcached

- add shared memory store

- add way of getting cache sizes out (what did I mean by this?)

- honour function strategy directives in config

- honour function stratgey parameter in code

- add option to conflate both scalar and list context results if the
  function returns equivalent data in either case

- add more POD for all packages

- add manual POD

- add cookbook for common use-cases

- enhance MemoryLRU to not store objects larger than some maximum size

- enhance MemoryLRU, or add another class that allows us to store a maximum
  number of objects rather than size

- look for other neat Cache::* classes that we might be able to simply add

- add multi-level caching