Architecture-specific backends?

[hdevalence]

Does it fit with the goals of this crate to have architecture-specific backends? For instance, a specialized NEON backend for mobile or embedded devices, or an ADX backend for x86. This conflicts with some stated goals of the crate (no unsafe code), and would require some planning on how to abstract over the backend, so I wanted to check first. It is totally reasonable for the strategy to be to instead provide a pure-rust, all-safe-code implementation as is the case now.

[ebfull]

I think I am okay with adding new backends as long as they are opt-in (via feature flags) but I haven't received much feedback from others about it. I wanted to see how fast we could get it without unsafe, and then go from there.