* Add radix2 FFT
Created a dynamic implementation of the radix - 2 Fast Fourier Transform for fast polynomial multiplication.
Reference: https://en.wikipedia.org/wiki/Cooley%E2%80%93Tukey_FFT_algorithm#The_radix-2_DIT_case
* Rename radix2_FFT.py to radix2_fft.py
* Update radix2_fft printing
Improved the printing method with f.prefix and String.join()
* __str__ method update
* Turned the tests into doctests
