Ready for review: new std.uni

[jerro]

> I.e. D's approach is to fix the language to support vector 
> semantics, rather than trying to back-asswards fit it into the 
> optimizer.

I agree that adding SIMD types and operations to the languages is 
a better approach than autovectorization. I'd just like to point 
out that DMD's backend still has serious problems regarding SIMD 
support, which makes getting SIMD code to work with DMD a pain. 
For example, see those two bugs:

http://d.puremagic.com/issues/show_bug.cgi?id=9304
http://d.puremagic.com/issues/show_bug.cgi?id=9200

I don't know how much work it is to fix those issues and any 
similar ones, but I think this is relevant to the discussion in 
this thread, since GCC and LLVM backends don't have those 
problems.