Close audio stream to fix memory leaks

Running 'stinkeedemo' with valgrind revealed that some memory was not
properly deallocated.  It turns out I was not using the PortAudio API
correctly.  The stream must still be closed (Pa_CloseStream) to release
all data; stopping the audio stream (Pa_StopStream) and terminating
PortAudio (Pa_Terminate) is not enough.