Add MSVC compiler support

[thiekus]

Hi, your conversion functions was good, but it can't be compiled under Microsoft Visual C++ compilers. Fortunately, the workarounds seems trivial and no codes other than macro and include declarations was changed.

• For include, MSVC doesn't have x86intrin.h header but it has emmintrin.h for same exact things.
• For SSE2 detection, MSVC also doesn't have __SSE2__ macro, but I use platform detection instead like _M_IX86_FP for 32bit as documentation and defaults if 64bit compiler was used. Also use _YUVRGB_SSE2_ macro for SSE2 compiler detection support rather than directly use __SSE2__ because of that.

At least, It works for me under MSVC 2015 although needs for more testing.

[descampsa]

Hey, Thanks for your pull request, i have commited a modified version (ee78934c8d542e8402bcb6eef7259217a6f859bc)

emmintrin.h should be portable for all platforms, so I have just included it. I did reuse your macro for SSE2 detection.

Untested with MSVC.