Implement filters on ppc64le with actual Altivec-SIMD instructions

[kif]

For now, the code is just auto-translated from SSE2. Here are some hints on how to do it properly:

For byte-shuffle it looks straights forwards: http://mirror.informatimago.com/next/developer.apple.com/hardware/ve/algorithms.html#byte_swap

For bit-shuffle, Initial explanation in: https://mischasan.wordpress.com/2011/07/24/what-is-sse-good-for-transposing-a-bit-matrix/ But I did not find (yet) an Altivec implementation