Complex numbers

[dy]

Implement dsp.js' FFT for complex numbers.

[rreusser]

As for FFT of real-valued input, in an audio context it makes perfect sense, but these lines seem maybe like they could be omitted since it's really just a one-liner to perform outside the function.

Which is to say, the FT(real-valued input) = complex valued output, so it doesn't seem strictly necessary to throw away half of the information that may be perfectly useful.