Add shuffles

[gquintin]

First, size agnostic shuffles, such as reverse, unpack, zip, unzip, ... will be added. Then it seems that (to be confirmed) all supported and yet to be supported architecture by NSIMD have SIMD vector lengths multiple of 128 bits. Therefore custom shuffles whose pattern is 128-bits wide can be repeated on all 128-bits lanes of a SIMD vector which make thoses shuffles also length agnostic. In any case one can follow the same reasoning on 64-bits patterns as SIMD vector length are, a priori, multiple of 64 bits which is sizeof(float64_t) * 8.