Actual fix for multiple filter sets in AudioFilterBiquad

My manipulation of the contents of *data instead of the value of data
itself was foolish at best - forgot to leave the * off for my intent.
Stereo peak meter using AudioPeak

Simplistic visual peak meter just outputs to terminal.
re-trim the comments in the example.

modified an older 'detached' copy of the example source to try multiple
filters out and didn't notice the old comments till reviewing later.
Mono peak meter using Analog in/out & AudioPeak

Untested, will test it personally in next couple of days but sincerely
expect it will work so committing.

Todo: Test properly. Improve comments and possibly link to wiring
example(s).
cosmetic change

I am tired of seeing Serial.begin(9600); where 9600 is not going to be
used at all. Can Serial.begin(Serial.baud()); be acceptable?
Merge pull request #13 from robsoles/master

Actual fix for multiple filter sets in AudioFilterBiquad