Check FFT algorithm for average RSSI calculation

[BlackWolf]

Currently, we calculate the average RSSI of a BT connection via an moving average.

This is good, but a FFT might be a better solution - although more difficult to implement.

See: https://developer.apple.com/library/mac/documentation/Performance/Conceptual/vDSP_Programming_Guide/UsingFourierTransforms/UsingFourierTransforms.html

http://www.tu-chemnitz.de/informatik/ThIS/downloads/courses/ws02/datkom/Fouriertransformation.pdf

http://paulbourke.net/miscellaneous/dft/

http://stackoverflow.com/questions/10820488/iphone-accelerate-framework-fft-vs-matlab-fft

https://github.com/hoddez/FFTAccelerate