added optimization for radix 2
added optimization for radix 2

### testing SNR for  1024 point FFTs
#### DOUBLE
snr_t2f = 296.29
snr_f2t = 314.48
#### FLOAT
snr_t2f = 146.48
snr_f2t = 143.03
#### SHORT
snr_t2f = -30.269
snr_f2t = -60.442

#### timing 10000 x 1024 point FFTs
#### DOUBLE
Elapsed:0:02.77 user:2.22 sys:0.13
#### FLOAT
Elapsed:0:01.65 user:1.35 sys:0.07
#### SHORT
Elapsed:0:02.44 user:2.00 sys:0.06

sf-is-evil/kissfft,sf-is-evil/kissfft,pemryan/kissFFT,pemryan/kissFFT,pemryan/kissFFT,pemryan/kissFFT,sf-is-evil/kissfft,sf-is-evil/kissfft