Check out an account from the pool

An account in the project that matches every filter given, that nobody else has checked out, and that lives past the hold: the least recently used first. It's yours for minutes (default 10, at most 60): nobody else can check it out until you return it or the time runs out, which frees it on its own. Use the checkout.token to extend or return it. 409 when every matching account is checked out (saying when the first comes free), 404 when none match. Tag accounts with their state (verified, premium…) to make pools.