Please help to move forward with ndslice

[Ilya Yaroshenko via Digitalmars-d]

Hello,

I found a way how to correctly implement multidimensional 
functional map for ndslices and for packed ndslices (tensors 
composed of tensors). It allows
  1. a compiler to use vectorisation with SIMD instructions like 
`fabs` or `sqrt` for example. But first [1] should be merged
  2. to manage mapped ndslices as common ndslices.
In additional the future ndmap abstraction has zero computational 
cost.

The are 6 ndslice PRs, which should be merged first [1]. Please 
help to review and merge this. They does not contain any new API 
names, but optimizations and small API enhancements, which was 
delayed before because I wanted to get enough experience with 
ndslice first.

ndslice is in experimental and it is the most generic package in 
Phobos along with new regex. Regex has a lot CTFE-able magic, 
ndslice operates with abstract entities. Feel free to ask 
questions if you want to have more detailed imagination about 
implementation.

[1] 
https://github.com/dlang/phobos/pulls?q=is%3Aopen+is%3Apr+author%3A9il+label%3Andslice

Thank you and best regards,
Ilya