blocking i/o not implemented for directsound

[rossb]

ReadStream? and WriteStream? are not implemented for DirectSound?. DirectSound? already provides ring buffers, and methods for querying their current state, so the main thing which is needed is to set up a timer to wake up the ReadStream?() and WriteStream?() functions when they are blocking.

One way to do this would be to write a high-precision sleep function which sets up a multimedia timer to signal an Event object, and then to block on the even object (also use a timeout to ensure the event object doesn't block forever). ReadStream/WriteStream? would sleep for long enough that they whole buffer space they are hoping to fill gets filled (or perhaps some fraction of the ringbuffer size.

[rossb]

duplicate of #56