Changed:

- Algorithm to determine `time_low` and `clock_seq` of UUIDv1.
  - `clock_seq` is now quite stable and is incremented only when the
    system clock is rewound or, in a remote chance, when too many IDs
    are generated within a millisecond. Instead, `time_low`'s pseudo
    sub-millisecond fraction is now more aggressively exploited as a
    monotonic counter to order IDs generated within a millisecond.