v3.0.0

Summary of changes since v2.0.0:

• Added Alire support.
• Refactoring to bring the code up-to-date with the latest versions of GNAT and GNATprove tools (#17), including numerous style and compile check fixes.
• Moved from Travis CI to GitHub Actions.
• Bug fixes:
  • Fixed incorrect parallel hash outputs when building using SSE2 instructions (#19).
  • Fixed a precondition for Keccak.Generic_MonkeyWrap.Init that was too restrictive.