Avx (rust-lang#90)

* avx: _mm256_andnot_pd, _mm256_andnot_ps

* avx: _mm256_blendv_pd

* avx: _mm256_blend_pd with no assert_instr

With assert_instr: too many instructions in the disassembly

* avx: _mm256_blendv_ps

* avx: _mm256_hadd_pd

* avx: _mm256_hadd_ps

* avx: _mm256_hsub_pd

* avx: _mm256_hsub_ps

* avx: _mm256_xor_pd

* avx: _mm256_xor_ps

* avx: _mm256_cvtepi32_pd

* avx: _mm256_cvtepi32_ps

* avx: _mm256_cvtpd_ps

* avx: _mm256_cvtps_epi32

* avx: _mm256_cvtps_pd

* avx: _mm256_cvttpd_epi32

* avx: _mm256_cvtpd_epi32

* avx: replace simd_cast by proper instrunction

* avx: _mm256_cvttps_epi32

* avx: _mm256_extractf128_ps, _mm256_undefined_ps

* avx: _mm256_extractf128_pd, _mm256_undefined_pd

* avx: _mm256_extractf128_si256, _mm256_undefined_si256

* avx: _mm256_extract_epi8

* avx: _mm256_extract_epi16

* avx: _mm256_extract_epi32

* avx: _mm256_extract_epi64

* avx: _mm256_zeroall

* avx: _mm256_zeroupper

* avx: _mm256_permutevar_ps

* avx: _mm_permutevar_ps

* avx: replace simd_cast by as_*

* avx: _mm256_permute_ps

* avx: _mm256_dp_ps

* avx: _mm256_shuffle_pd

* avx: _mm256_shuffle_pd, wrong instruction generated

* implement _mm256_hadd_ps and _mm256_hadd_pd

* avx: implement _mm256_hsub_pd and _mm256_hsub_ps

* assert_instr: raise the limit up to 30 instructions

Author: gwenn