Break reading and enqueueing of audio buffers into two steps so that errors in enqueueing can be distinguished for errors in reading.  Errors in enqueueing signal a downstream decoder error.  Add logic to gracefully recover from downstream decoder errors.

NxPlayer: Fix an error I introduced:  Need to pass through final buffer even if is it zero length because it contains the end of audio stream flag

Audio: Change how the end of the audio stream is detected by the leaf audio component.  This used by be done by looking for the first partial buffer.  That does not work with the in-place sub-sampling performed by the PCM decoder:  That always reduces the size of the buffer so that all buffers only partially filled by the time they get to the leaf.  Now, a flag is set in the audio buffer flags set to indicate the final buffer in the stream.

dd support for a USB keyboard as the NxConsole and text widget input.  Not fully functional as of this initial check-in.  Basic functionality is there, but there are conditions were the keyboard gets lost.

NxPlayer needs to set curbyte field to zero before enqueuing a buffer.  Otherwise, it looks like beginning of the buffer has already been consumed

Audio:  Add hooks for fast-forward and rewind needed by CMediaPlayer; add hooks for equalizer settings needed by the WM8904

NxWM: Beginning integration of NxPlayer into Nxwm::MediaPlayer. Gets handle, sets device, and releases handle.  Lots more to be done

NxWM: Increase default priority of mouse and keyboard listener threads. Does not seem to make any difference but still seems like a good idea