* Added bitexact implementations of _BitScanForward64 and _BitScanReverse64 for VS2019 32-bit builds
* Added bitexact implementations of _umul128 for VS2019 x86, arm, arm64 builds
* Implement mul_overflow for VS2019 arm64 builds
+ implement mul_overflow using __umulh (msvc/clang results: https://godbolt.org/z/smRwA7)
* Added Win32 for VS2019 to .appveyor.yml
* Update amalgamated headers (fix x86 builds with VS2019)
Only the simdjson library should optionally depend on threads,
the executables that link to simdjson will get the dependency
indirectly.
* add option for controlling threads (default is on)
* add CI testing with threading on/off for msvc, gcc and clang
* fix an unrelated copy paste comment error in the cirlce ci build conf
* Hiding the runtime dispatch pointer in a source file so it is not an exported symbol
* Disabling hard failure on style check.
* Fixes https://github.com/lemire/simdjson/issues/250
Daniel Lemire
John Keiser
PavelP
Paul Dreik