Package locker provides a mechanism for creating finer-grained locking to help free up more global locks to handle other tasks. The implementation looks close to a sync.Mutex, however the user must provide a reference to use to refer to the underlying lock when locking and unlocking, and unlock may generate an error. If a lock with a given name does not exist when `Lock` is called, one is created. Lock references are automatically cleaned up on `Unlock` if nothing else is waiting for the lock.