0.5 - ZoneManager allows dynamic creation of TimeZone

• 0.5 (2019-07-21, TB DB version 2019a, beta)
  • Remove over-engineered SystemClockHeartbeatLoop and
    SystemClockHeartbeatLoop and replace with just a call to
    SystemClock::keepAlive().
  • Remove overly complex ManualZoneProcessor and merge most of its
    functionality directly into the TimeZone using kTypeManual. We lose
    the manual abbreviations provided by ManualZoneProcessor but the
    simplification of using just the TimeZone object without an extra object
    seems worth it.
  • Add a stable zoneId to ZoneInfo that identifies a zone. It is
    formed using a hash of the fully qualified zone name. The
    tzcompiler.py generator script will detect hash collisions and create an
    alternate hash.
  • Rename old ZoneManager as the ZoneRegistrar, and
    repurpose ZoneManager as the TimeZone factory, which keeps an internal
    cache of ZoneProcessor. TimeZone objects can be dynamically bound to
    ZoneProcessor objects using createForZoneInfo(),
    createForZoneName(), `createForZoneId().
  • Add TimeZoneData data struct to allow serialization of a TimeZone object
    as a zoneId so that it can be reconstructed using
    ZoneManger::createForTimeZoneData().
  • Rename ZoneSpecifier to ZoneProcessor to describe its functionality
    better. ZoneInfo is now passed directly into the TimeZone object using
    the TimeZone::forZoneInfo() factory method, with the ZoneProcessor
    acting as a helper object.