Draft: Add AVXStdMat Implementation

Issue/feature addressed

The current SerialStdMat implementation does not make good use of the cache and AVX capability in CPU.

Proposed solution

Change SerialStdMat to a cache-friendly implementation SerialAVXStdMat with a similar design as the SerialAVXSumFac

Implementation

• Change DataType to simd_t ;
• Interleave data layout to simd_t::width;
• Replace BLAS with manual for loops;
• Maybe use BOOST PP to switch to a specific size operator;

Tests

Suggested reviewers

@ssherw @CFD-Xing

Please suggest any people who would be appropriate to review your code.

Notes

Please add any other information that could be useful for reviewers.

Checklist

• Functions and classes, or changes to them, are documented.
• User guide/documentation is updated.
• Changelog is updated.
• Suitable tests added for new functionality.
• Contributed code is correctly formatted. (See the contributing guidelines).
• License added to any new files.
• No extraneous files have been added (e.g. compiler output or test data files).