Experimental SIMD support

[ManevilleF]

Addresses #59

Work done:

SIMD

• Added experimental SIMD support behind simd feature:
  • The Sum implementation will use SIMD
  • Added the following functions:
  • Hex::simd_add4
  • Hex::simd_add8
  • Hex::simd_min4
  • Hex::simd_min8
  • Hex::simd_max4
  • Hex::simd_max8

Other

• Dropped legacy ser_de feature, use serde insted
• Added new methods for Hex iterators:
  • min which computes the minimum value
  • max which computes the max value

Thoughts

I added a benchmark that shows that the SIMD sum is slower than a regular sum in release mode. So either my Mac is not supported by wide simd operations and is falling back to regular slower sums, or I'm using the crate wrong.

Also the min/ max methods are not using SIMD at all, wide provides them but the implementation is not using simd optimizations.

I'm not sure that it's worth it.

[alice-i-cecile]

Yeah without benchmarks showing clear performance gains I definitely wouldn't add this.