Release 0.176.0

Compiler support

• Update to Supported compilers
  documentation to reflect the compilers that are currently in continuous integration testing.

• Support for some ancient compilers, in particular g++ 4.8 and 4.9, has been dropped.

• Accepted pr #519 to support build with with llvm-toolset-7 on CentOS 7.

• We (and users) have seen some compilation errors with tests of std::scoped_allocator_adaptor using our sample stateful allocator FreeListAllocator
  in versions of clang predating version 11, and versions of g++ predating version 10. We've therefore excluded these tests when testing with
  the older compilers.

Enhancements

• basic_json now supports using C++ 17 structured binding, so you can write

for (const auto& [key, value] : j.object_range())
{
    std::cout << key << " => " << value << std::endl;
}

• Addressed issue #509 of over allocating memory due to alignment constraints through pr #510

jsonschema extension defect fixes:

• Fixed issue #520 where enabling format validation resulted in a premature abort to validation

• Addressed issue #521 so that jsonschema now supports big integers

Other defect fixes:

• Resolved #518 about CUDA and int128 and float 128