Investigate coefficient smoothing

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The docs suggest you can use Dsp::SmoothedFilterDesign instead of Dsp::FilterDesign. It isn't clear if this work is on the master branch of the lib though.

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e.g.

	//	Dsp::SmoothedFilterDesign<Dsp::Elliptic::Design::LowPass<200>,2> mFilter { 1024 };
	// ^ max-order 200, stereo, 1024 samples of smoothing