wip/fxt 2019.03.09 NetBSD

fxt is a library package (coming as C++ source code) containing various algorithms for:

• Fast Fourier Transform (FFT) incl. real-valued,
• multidimensional and weighted variants.
• Fast Hartley Transform (FHT)
• Number Theoretic Transform (NTT), Fast Walsh Transform.
• Convolution (cyclic, linear and weighted),
• correlation and power spectrum.
• Fast Haar Transform, Fast Wavelet Transform
• Mass storage convolution and fast multiplication routines.
• Sine- and cosine transform (DCT, DST), Fast Z-Transform (FZT)