Added support for biquad, parametric, and multi-band filter eq

Implements a specific feature request from the HiFi team. This patch implements a  multi-band parametric eq, directly integrated into the interface client app.   By request, the eq is applied immediately before loop-back on the output of the capture-device; however, it may be used anywhere.

Two new files, AudioFilter.h/.cpp contain the actual filter DSP code.  The remaining changes in Audio.h/.cpp and Menu.h/.cpp are essentially just glue for the app UI.

The design is completely general purpose, and is trivial to extend to add high/low pass, high/low shelf, all-pass and other biquad filter types by simply adding new coefficient sets.   See http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt for details.   For this patch, a flexible parametric/peaking EQ type is implemented with support for variable center frequency, gain, and resonance/q.   3 bands of parametric EQ have been integrated into the capture-device path.

This proposed design also makes makes it easy trivial to aggregate and manage banks of filters using c++ templates.  See template< typename T, const int N> class AudioFilterBank.  

To test/enable the feature, enable:
  'Developer:Audio Debugging Tools:Audio Filter Bank'
Four sample 3-band parametric filter profile response curves may be previewed at:
 ' 'Developer:Audio Debugging Tools:Audio Filter Options:'

Craig Hansen-Sturm
Indeed !