SIMDPP_HAS_SHUFFLE_BYTES16 is missing

[xugng]

shuffle_bytes16 is not available on all instruction sets. Using it on unsupported instruction sets can result in errors that are difficult to track. Can we check availability via SIMDPP_HAS_SHUFFLE_BYTES16 macro?

[p12tic]

Thanks for the suggestion. The proposal makes sense. I guess all of shuffle_bytes16, shuffle_zbytes16, permute_bytes16 and permute_zbytes16 should be handled by that macro as any kind of byte shuffle instruction allows to implement all four functions.