Add support for Visual Studio 2019

[stevenhoving]

Currently the way the CMake infra is setup it does not 'support' Visual Studio. Now I have changes to make that work. All that is needed is to clean things up and restructure it a bit. On top of that I have a couple of other things pending that are required for MSVC.

Tasks:

• [ ] Add CMake support for Visual Studio (aka make the gcc/clang specific things conditional)
• [ ] Add /permissive- for Visual Studio
• [ ] Create cross platform abstraction for __tzcnt_u64 (I think on msvc its _BitScanForward64)
• [ ] Use alternative method for const volatile __m128i value in bench.cc (to avoid them being optimized away)
• [ ] Fix 'non standard' use of arithmetic operators on __m128i types (a = b - c becomes a = _mm_sub_epi8(b, c))
• [ ] Use [[likely]] attribute instead of likely / unlikely macro
• [ ] Fix std::sprintf not using "%lld" to string format a long long type

[KholdStare]

Hey Steven! Sure, I don't mind at all. Perhaps I can work on setting up Travis CI or something like that to make sure all the compilers are supported. I primarily work on Linux so testing MSVC is awkward for me