modified an older 'detached' copy of the example source to try multiple
filters out and didn't notice the old comments till reviewing later.

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.

added last of dap 'bits' to control_sgtl5000.* and include an example
for bass enhance, need to make one for surround stuff.

Added
AudioControlSGTL5000::dap_avc(..);
AudioControlSGTL5000::dap_avc_enable(..);

SGTL5000_Specific/dap_avc_agc example sketch

Also added 'public domain...' line to all my examples.

The 'tone' filter examples are both using calcBiquad(..); but one uses
AudioFilterBiquad and other uses SGTL5000 PEQ filters. Had included code
for volume level control optionally and decided to drop it from both.