Macro dispatch

macro_rules! dispatch {
    ($mach:ident, $MTy:ident, { $([$pub:tt$(($krate:tt))*])* fn $name:ident($($arg:ident: $argty:ty),* $(,)*) -> $ret:ty $body:block }) => { ... };
    ($mach:ident, $MTy:ident, { $([$pub:tt $(($krate:tt))*])* fn $name:ident($($arg:ident: $argty:ty),* $(,)*) $body:block }) => { ... };
}

Generate the full set of optimized implementations to take advantage of the most important hardware feature sets.

This dispatcher is suitable for maximizing throughput.