Issue 46

Pushed 558c9c213852de9b442a4a7f542408c3c8194a45 to the branch, as agreed.
Also, now I remember, discussing something along those lines with Chris... So that the `TimeSource` (or something) could be injected in the `Store` directly, so that the `ExpiryPolicy`, honored by the `Cache` can rely on the "same wall clock" or any other clock...