Fix #477 - Reimplement splatted/non-splatted reduction properly

- Added generic all_reduce function and tests:
  all_reduce implements a butterfly reduction/broadcast algorithm
  using shuffle and any generic binary operator. This can be done
  generically on all SIMD extensions. In emulation mode, we still
  go by a recursive fold over vector elements to limit the number
  of useless MOVs. AVX use a specific implementation relying on
  _mm256_permute for 32 and 64 bits types.

- Fixed sum/splatted_sum and tests:
  (S)SSE3 version have been removed as it was suboptimal.
  Reported benchmark goes from 2.8 to 1.9 cycles/points.

- Fixed prod,minimum,maximum and splatted_ functions and tests:
  All are implemented as a call to all_reduce + a value extraction.

- Fixed reduction/all_reduction for complex and dry:
  dry support is only required explicitly as complex is now catched
  automatically by the common SIMD version. dry version use a back
  and forth bitwise-cast implementation.

- Removed useless files

Next to this and to have all_reduce working in all cases, the following changes
impact shuffle:
- Added support for complex shuffle by simply shuffling real and imaginary parts.
- Added support for logical shuffle by bitwise_casting back and forth.
- Fixed shuffle on SSSE3 for real to use normal SSE2 shuffle for performance reasons

Finally, some files in core/ have  been amended because they lacked either some
include paths or explicit qualification on 4.4.