start on SIMD documentation

[Walter Bright]

On 1/16/2012 8:38 AM, Andrei Alexandrescu wrote:
> Either approach should work perfectly fine; it "cheats in style" by using an
> existing language construct that exactly matches the special-cased capability.
> The current approach cheats badly - it messes with the language's fabric by
> defining a construct that's not a function but looks like one.

You're right, it is cheating.

> I'd be in your debt if you could at least do the right thing when defining new
> intrinsics.

We can talk about that some more. At some point, there's going to have to be 
some compiler magic going on.