2021-08-29 version 4.0.0 for C++

Improve zone alignment logic (#965)
Fix v1 unpack logic for STR and BIN (#957, #951)
Fix UB on memcmp with size 0 (#954)
Fix iovec name conflict (#952)
Add std::array<std::byte> std::span<char> std::span<unsigned char> std::span<std::byte> adaptors (#951)
Improve documents (#918, #919, #951)
Improve tests (#916)
Introduce BOOST_ASSERT (#898)
Improve build system (#897, #905, #924, #951)
Improve Boost.Fusion support (#894)
Check nullptr before call memcpy (#891)
Refine and bugfix std::chrono::time_point adaptor (#888, #893)
Improve CI (#884, #892, #895, #951, #955)

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