Added test for Cavern's FFT

[VoidXH]

Test implemented for Cavern's fully .NET FFT which rivals real FFTs at large sizes:

FFT size: 2^14 (16384)
  Repeat: 80

[11/11] Done

Exocortex (real):  1.0  [min:  149.54, max:  174.49, mean:  152.50, stddev:    3.69]
          Cavern:  1.4  [min:  204.24, max:  249.82, mean:  213.16, stddev:   10.16]
   NWaves (real):  1.5  [min:  220.79, max:  272.86, mean:  226.15, stddev:    7.82]
   Lomont (real):  1.8  [min:  273.96, max:  292.92, mean:  279.43, stddev:    3.88]
          Accord:  3.0  [min:  401.09, max:  693.31, mean:  462.60, stddev:   73.43]
          NWaves:  3.1  [min:  465.31, max:  518.50, mean:  473.22, stddev:    8.66]
          NAudio:  3.8  [min:  560.12, max:  614.02, mean:  573.28, stddev:    8.90]
       Exocortex:  4.9  [min:  737.58, max:  759.13, mean:  747.29, stddev:    4.24]
          Lomont:  5.0  [min:  751.17, max:  772.21, mean:  760.71, stddev:    4.65]
          AForge:  5.7  [min:  833.21, max: 1024.35, mean:  869.97, stddev:   31.89]
        Math.NET:  7.1  [min: 1024.33, max: 1198.71, mean: 1084.55, stddev:   28.94]

Timing in microseconds.

[wo80]

Sorry for late response, nearly forgot about this one...

Very interesting use of unsafe and SIMD. I like it!