Features for core integration

[jeffmiles63]

 1. SIMD aware layouts
 2. Execution Space defaults for storage and ABI types
 3. view and deep_copy extensions for SIMD

[ibaned]

shouldn't this be something that is addressed in the kokkos/kokkos repository after these headers are merged into it? We can't really develop things on top of Kokkos execution spaces in this repository.

[crtrott]

We are starting to work on this for real. Couple things we need to change:

• filenames/includes: currently we include files like "pack.hpp" right from the global include scope
  • one option: rename
  • second option: include directories i.e. you include something like "some-include-path/simd.hpp"
• include guards: if we want this to be able to live also standalone we need to resolve the issue of what happens if both Kokkos and the external thing are used

There is probably interest to have this available via DESUL we need to discuss that.

• we think that we might need to use include guards instead of pragma once
• macros like SIMD_PRAGMA and SIMD_ALWAYS_INLINE are probably a bit too generic