Added a test to compute 2D DFTs.
Computes test using both real and complex FFTs, cleaned up comments.
Added vectorizing schedule for part of the algorithm.
Improved zip/transpose algorithms, added a decently vectorizing schedule.
Removed old helper functions.
Fixed boneheaded error.
Optimized real FFT by zipping columns from each half of the input (instead of zipping pairs of adjacent columns), optimized complex FFT by performing transpose before each FFT.
Computed twiddle factors statically.
Zipped columns from half of the FFT in inverse real transforms.
Merge pull request #363 from halide/fft_test

FFT test