PDL::Filter::Linear - linear filtering for PDL

	$a = new PDL::Filter::Linear(
		{Weights => $v,
		 Point => 10});

	$b = new PDL::Filter::Gaussian(15,2); # 15 points, 2 std devn.

	($pred,$corrslic) = $a->predict($dat);

A wrapper for generic linear filters. Just for convenience. This should in the future use DataPresenter.

Also, this class should at some point learn to do FFT whenever it is useful.