Error propagation from state_update()

Now generate Kaiser-Bessel filters

Use code adapted from

	http://arc.id.au/FilterDesign.html

and

	http://arc.id.au/dspUtils-10.js

to generate filters for given parameters. This permits adaptation to
different sample rates, and will permit tuning of filter parameters to
improve detection accuracy.

Decodes WAVs with horrid precision

At 8kHz 16bit PCM, gets about 81% accuracy decoding a string of recorded
Z's -- but the original recording seems to have had some errors or
truncated characters, so there may be upstream problems as well. Many
improvements to be made.