- Removed 'x86-64-modern' as a valid target architecture in the Makefile,
  replaced by 'x86-64-popcnt'
- Cleaned up the King safety eval function by inverting the conditional and
  making it an early return instead
- Updated the UciOptionFields declaration in main.c so that it uses named fields
  for the sake of clarity
- Updated the release.sh script because of the recent changes to the Makefile
  behavior, and also made the Linux builds usable by using static linkage
- Renamed the contributing help file so that it gets detected correctly by
  GitHub
- Extended the 'id author' to reference all direct code contributors via the
  added AUTHORS file

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