Previously, negative amplitudes were clamped to zero.
Now, they are allowed to range from -ALMOST_ONE to +ALMOST_ONE.
This is useful in certain circumstances, such as using synthio
to create CV-like outputs that can be positive or negative, by
using the amplitude property of the note.
A note can be placed in the center (panning=0) or moved to just the left
(panning=1) or right (panning=-1) channels. Fractional panning values
place it partially in both channels.
This class allows much more expressive sound synthesis:
* tremolo & vibrato
* arbitrary frequency
* different evelope & waveform per note
* all properties dynamically settable from Python code
