docs: kithara-dsp spectrum, downmix and sum of squares; kithara-waveform page; analysis on kithara-dsp
docs(dsp): biquad cascade, interpolation and Glide on kithara-dsp kithara-dsp gains filter::Biquad, the biquad crate's designs, interp::interpolate and interp::RateRamp; kithara-resampler's Glide runs on them and drops apple-accelerate. Both pages are reviewed at 4ba0bb5bc; the resampler page's stale Resample<S> paragraph now names kithara-decode's DecoderResamplerConfig<B>.
docs(dsp): kithara-dsp layout and sanitize kernels, firewheel facade