Move Reducers out of Experimental namespace

[ibaned]

No description provided.

[dalabre]

@ibaned This means removing them from ```namespace Experimental { .... }''', thus leaving them in mostly '''namespace Kokkos { }''' ?

....and these are all the reducer functions: md_parallel_for(?), md_parallel_reduce, Sum, Prod, Min, ...etc?

[ibaned]

Yes. You can also add the following to help ease the transition on applications:

namespace Experimental {
  using Kokkos::Min;
  ...
}

This allows Kokkos::Experimental::Min to still compile.

md_parallel_for and md_parallel_reduce are unrelated, in fact they should be removed, but thats @ndellingwood 's responsibility. The reducers are Sum, Prod, Min, etc.