Better interface for Piezo Buzzer sound

[Matt5sean3]

A desire for this feature was expressed after the meeting. This interface would allow playing more complex sound over the Piezo Buzzer than just a beep and retrieving sound snippets in the flash memory.

[Matt5sean3]

The current interface for Piezo Buzzer sound is available from "assets.h"

/** Toggles the electric current to speaker if set number of ticks have passed.
 * If the current note is done, calls callback for the current audio asset.
 */
void doAudio();
/**
 * Tells timer interrupt to play a note.
 * @param [in] freq The note frequency (# of timer ticks between pulses)
 *        <needed here> formula for HZ -> freq value
 * @param [in] dur The duration of the note, in timer ticks
 */
void setNote(unsigned short freq, unsigned short dur) ;

/* void setBeep(unsigned short freq); */ /* not implemented */

/** Callback for setting next note when current note is complete. */
void nextNote_cb(unsigned char assetId, int frame);
void nextMIDI_cb(unsigned char assetId, int frame) ;

[Matt5sean3]

nextNote_cb and nextMIDI_cb don't appear to actually be used anywhere.