It has a slight color cast to it at the moment, I believe due to
incorrect color space conversions, not because of the upsampling
method itself. So Meng upsampling is still the active method
at the moment.
Rust 1.27 stablized a variety of cpu intrinsics, including SIMD
on x86/64 platforms. This commit moves to using those intrinsics
for the optimized Float4 implementation. This means Psychopath
now compiles on stable Rust with all optimizations. Yay!
