v1.5 - officially support STM32; upgrade to TZ DB 2021a; implement fat Links

• 1.5
  • Use binary search for both ZoneManager::createForZoneName() and
    ZoneManager::createForZoneId().
    • Previously, the zone_registry.cpp was sorted by zoneName, so only
      the createForZoneName() could use the binary search. The new
      solution sorts the zone_registry.cpp entries by zoneId instead of
      zoneName. The createForZoneId() can use the binary search
      algorith.
    • The createForZoneName() can also use the binary search because
      the zoneName is converted dynamically to its zoneId using the same
      djb2 hash algorithm used by the tzcompiler.py. If there is a match,
      a final verification against the exact zoneName is performed to make
      sure that there was no hash collision.
    • Updated AutoBenchmark.ino to determine that a binary search on the
      266 zones in zonedb/zone_registry.cpp is 9-10X faster (on average)
      than a linear search through the same list. (Linear search takes ~190
      iterations; binary search takes ~9 iterations.)
  • Upgrade Link entries to be "fat links".
    • Links become essentially identical to Zone entries, with references to
      the same underlying ZoneEra records.
    • Add kZoneAndLinkRegistry[] array in zone_registry.h that contains
      all Links as well as Zones.
    • Add "Zones and Links" section in USER_GUIDE.md.
  • Implement zoneName compression using ace_common::KString.
    • Saves about 1500-2300 bytes for basic zonedb info files, and
      2500-3400 bytes for extended zonedbx info files.
  • Potentially Breaking Change: Remove transitionBufSize from
    ZoneInfo struct, and migrate to kZoneBufSize{xxx} constants in the
    zone_infos.h files.
    • This was used only in validation tests under tests/validation and
      only for Extended{xxx} tests. Saves 1 byte per Zone on 8-bit
      processors, but none on 32-bit processors due to 4-byte alignment.
    • This should have no impact on client code since this field was used
      only for validation testing.
  • API Breaking Change: Replace BasicZone::name() and shortName()
    with printNameTo() and printShortNameTo(). Same with
    ExtendedZone::name() and shortName(), replaced with printNameTo()
    and printShortNameTo().
    • After implementing zoneName compression, it was no longer possible to
      return a simple pointer to the name and shortName without using
      static memory buffers.
    • I expect almost no one to be using the BasicZone and ExtendedZone
      classes, since they are mostly useful for internal algorithms.
    • Client code that needs the old functionality can use
      BasicZone::printNameTo(Print&),
      BasicZone::printShortNameTo(Print&) (similarly for ExtendedZone)
      to print to a ace_common::PrintStr<> object, then extract the
      c-string using PrintStr::getCstr().
  • Update UnixHostDuino 0.4 to EpoxyDuino 0.5.
  • Explicitly blacklist megaAVR boards, and SAMD21 boards using
    arduino:samd Core >= 1.8.10.
    • This allows a helpful message to be shown to the user, instead of the
      pages and pages of compiler errors.
  • Update TZ Database to 2021a.
    • https://mm.icann.org/pipermail/tz-announce/2021-January/000065.html
    • "South Sudan changes from +03 to +02 on 2021-02-01 at 00:00."
  • Officially support STM32 and STM32duino after testing on STM32 Blue Pill.