Add Window class, to produce windows of different types (see Window::TYPES). Rendered windows with Gnuplot to verify.
Seperate each window type into its own class.
Remove Window class (superceded by separate window classes).
Add DFT class, which does forward DFT transform (inverse will come soon).
Add FIR class, for working with FIR filters.
Add SincFilter, a FIR filter that uses a windowed sinc function to perform lowpass and highpass filtering.
Add DualSincFilter, a FIR filter that performs bandpass and bandstop filtering.
Add utility classes for generating test signals, and linear/exponential scales.
Add DFT.inverse_dft.
Modify .forward_dft so it produces the entire output (including mirror image) by default. A skip_second_half falg can be set true to skip this mirror image and return an output half the size of input. Also, return array of complex values so it can be passed on to inverse_dft for a complete restoration to original signal.