deadly simplistic peak difference measuring object, after begin() just
goes through samples and find the maximum and minimum signed values,
natural behavior of begin() is to reset the max and min, member uint16_t
Dpp() returns maximum difference seen and .stop() does what it says.

I put the line I had moved into the loop the wrong side of the test
conditional.

I left 'end' in an undefined state before.

'data' needs to be reset inside the 'flag' controlled loop or
*undefined* behavior is likely when user sets 'flag' and loop repeats
without resetting 'data' to beginning of block.

adding surround and bass enhance controls

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

Cosmetic fixes to chorus and flange examples and synth_tonesweep (ignore AudioSynthToneSweep changes)

Add AVC control to control_sgtl5000.* and example

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

SGTL5000_Specific/dap_avc_agc example sketch

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

https://github.com/PaulStoffregen/Audio/pull/7

My own version of AudioSynthWaveform. Sine is generated with arm_sin_q15...

Conflicts:
	Audio.cpp
	Audio.h

Conflicts:
	Audio.cpp
	Audio.h

Some filter additions, some SGTL5000 additions

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.

I forgot to sync the changes relating to things like 'dac_vol_right(..)'
& 'dac_vol_left(..)' removed in favor of 'dac_vol(left,right)' instead;
applies to 'volume(..)', 'lo_lvl(..)' & 'dac_vol(..)'.

Changed method for setting level/gains for left & right from
'item_left(..); item_right(..);' style to 'volume(left,right)' style
instead.

removed 'route(..)' due not easily supportable atm. Updated
'dap_enable(..)' in lieu of route. Fixed dap_audio_eq_band(..) bad use
of unsigned. Changed 'updateCoefs(..)' so default behavior is not reset
other three elements of state.

Something wrong with my attempt to apply the math in the datasheet,
CHIP_LINE_OUT_VALUE is better set to 0x0505 rather than 0x0D0D.