Rust nstream variants

[hattom]

New PRK implementation checklist

Which kernels are implemented?

• [ ] synch_p2p (p2p)
• [ ] stencil
• [ ] transpose
• [ X ] nstream
• [ ] dgemm
• [ ] reduce
• [ ] sparse
• [ ] branch
• [ ] random
• [ ] refcount
• [ ] synch_global
• [ ] PIC
• [ ] AMR

Is Travis CI supported?

• [ X ] Yes
• [ ] No

If no, why not? (not tested)

There are many good reasons why Travis CI support may not be part of your PR. You or someone else can always add it later. In many cases, we will add it later

Documentation and build examples

If your implementation uses a new programming model that is not ubiquitious (i.e. included in the system compiler on most systems) then you need to provide a link to the appropriate documentation for a new user to install it, etc.

We strongly recommend that you add the appropriate features to make.defs.${toolchain} if appropriate.

[jeffhammond]

I'm happy to merge this any time. Please look at the comments first though.

[jeffhammond]

Thanks!