ssse3: add NEON implementations of _mm_shuffle_{epi8,pi8}
ssse3: add NEON implementations of _mm_shuffle_{epi8,pi8}

The new epi8 function is about an order of magnitude faster (I didn't
bother checking the pi8 one).  This should provide a huge speed-up for
LZSSE compression, which profiling showed was spending *lot* of time in
simde_mm_shuffle_epi8, as well as any other shuffle-heavy code.

nemequ/simde,nemequ/simde,nemequ/simde