Add benchmark against ooura FFT

[dean-shaff]

Benchmark against ooura. This implementation is very fast!

[j-funk]

Interesting, thank you. I will definitely look into it. I notice that Ooura's benchmarks are against some repositories that are not included here as well. It's been awhile since I was using FFTs, but I expect to be back at it in the coming months. In the meantime I will happily review/merge any work from yourself / community.