dense-linear-algebra: Add support for SIMD instructions

[Magalame]

SIMD instructions seem to be of great importance in the performances of a linear algebra library. The big question then is how to incorporate them to the rest of the library?

I've had some success with a fork of simd: https://github.com/Magalame/simd

Another question to solve would be how to:

• detect which instructions are available
• handle conditional compilation (https://www.reddit.com/r/haskell/comments/c64hbr/tweag_io_cpp_considered_harmful/)
• handle stream fusion when converting back and forth to simd vectors