Check bit 28 for AVX support

[Lynnesbian]

When checking for AVX support on x86 platforms, the code currently looks at bit 27 twice:

faster-hex/src/lib.rs

Lines 95 to 97 in a7ce51f

	let have_xsave = (proc_info_ecx >> 26) & 1 == 1;
	let have_osxsave = (proc_info_ecx >> 27) & 1 == 1;
	let have_avx = (proc_info_ecx >> 27) & 1 == 1;

Wikipedia's CPUID article states that the avx flag is in bit 28. This pull request changes the code to check bit 28 for AVX support instead of bit 27.

I ensured that all tests passed before committing.

[eval-exec]

Thank you, please also invite @elichai to review this pull request.

[eval-exec]

I think this PR is ready to merge.