Some filter additions, some SGTL5000 additions

added AudioBiquadFilter::
public:
void updateCoefs(int *source, bool noReset);
void updateCoefs(int *source);

added AudioControlSGTL5000::
private:
unsigned int modify(unsigned int reg, unsigned int val, unsigned int
iMask);

public:
unsigned int micGain(unsigned int n) { return modify(0x002A, n&3, 3); }
unsigned short lo_lvl_right(uint8_t n);
unsigned short lo_lvl_left(uint8_t n);
unsigned short lo_lvl(uint8_t n);
unsigned short dac_vol_right(float n);
unsigned short dac_vol_left(float n);
unsigned short dac_vol(float n);
unsigned short dap_mix_enable(uint8_t n);
unsigned short dap_enable(uint8_t n);
unsigned short dap_peqs(uint8_t n);
unsigned short dap_audio_eq(uint8_t n);
unsigned short dap_audio_eq_band(uint8_t bandNum, float n);
void dap_audio_eq_geq(float bass, float mid_bass, float midrange, float
mid_treble, float treble);
void dap_audio_eq_tone(float bass, float treble);
void load_peq(uint8_t filterNum, int *filterParameters);
void route(uint8_t via_i2s, uint8_t via_dap);
Fix SGTL5000 filter coefficent loader

load_peq(..); wasn't writing the INDEX and WR bits in
DAP_FILTER_COEF_ACCESS
Add delay to coefficient loader fix.

I thought the time taken to read back and then write zero back to the
DAP_FILTER_COEF_ACCESS WR bit would be enough but coefficients did not
load to the selected filter, tried 1ms delay instead still didn't work -
chances are that either not zero-ing or only zero-ing just before
writing the DAP_COEF_WR_xx_xSB registers would be fine but for now I'd
prefer to zero it sooner than later.
Revert line out level value

Something wrong with my attempt to apply the math in the datasheet,
CHIP_LINE_OUT_VALUE is better set to 0x0505 rather than 0x0D0D.
Various corrections and addition of calcBiquad(..);

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.
Added DAC & HP balance examples

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

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(..)'.
Added filter 'tone' examples and trimmed fat in balance 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.
Merge pull request #4 from robsoles/master

Some filter additions, some SGTL5000 additions