Performance improvements

Now uses a multi-threaded architecture.  "write" simply stores the
audio-buffer, while the background-thread handles writing this buffer to
Port Audio.  This way, the Javascript environment is no longer logged up
while "Pa_WriteStream" does its thing.

2.  Provides an option to disable microphone input if your application
is not using it.
Adds support for a ring of audio buffers

If you wish to have low latency (you can't go generate a large audio
buffer without interrupting frame rendering), but you also don't want
audio skips when your app does something intensive, you need a ring of
buffers.

The application fills one buffer a time via write, meanwhile the
background thread writes one buffer at a time back to port audio.  This
way, you have very short individual writes, but a lot of audio for the
background thread to pull from if your app locks up for a bit.
Includes a simple test-script which demonstrates real-time audio output, along with displaying microphone input.
Merge pull request #31 from anprogrammer/master

Performance/Parallel Processing improvements