-Added vzeroupper to satd macro to prevent AVX-SSE transition penalties int picture_x86.asm
-Fixed the order of registers in zero extend macro in picture_x86.asm
-Fixed SATD checkers test pattern in satd_tests.c
- Add our own Github fork of greatest as a submodule, in case we want to
improve it and push changes upstream easily in the future.
- Update existing unit tests to use greatest.
- Update Visual Studio project to remove traces of seatest and include greatest.