The ABM had an off-by-one error in the DMA buffer swapover. Instead of
setting the DMA address to the newly added buffer in active[], it set it
to the buffer that was currently running.
This would effectively disable the ping-pong and cause clicks/lost data.
Fixes#1491
Mimics the I2S/PWMAudio/Stream interface for ease of use.
* Fix non-32b DMA size transfer calculation in ABM
* Rename wasHolding to isHolding in the I2S/PWM
It is the **current** number of bits left, not the past number.
* Add commented microphone example
* Add docs
Use the PWM hardware to generate a signal suitable for filtering and
amplifying 16bps audio output.
Refactor the AudioBufferManager to allow sharing with I2S
Add example
