Macro safe_arch::extract_m128_from_m256

macro_rules! extract_m128_from_m256 {
    ($a:expr, $imm:expr) => { ... };
}

This is supported with target feature avx only.

Extracts an m128 from m256

let a = m256::from([9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0]);
let b = m128::from([13.0, 14.0, 15.0, 16.0]).to_array();
let c = extract_m128_from_m256!(a, 1).to_array();
assert_eq!(b, c);