Adding a `saveSoon` method to have the timings used for save colaescing all in one place.
Simpler implementation of the `closeDatabase` method.
Adding an accessor to PARDispatchQueue to query the number of timers currently scheduled.
Clarifying the expected state of the store when dealloc-ed. It turns out it will be in a consistent state no matter what, since the blocks used for saving and syncing will retain it beyond what other objects might do.