This adds retry processing back to the queue functions. queue_remove
should only be called after the head entry on the queue is processed
successfully.
Make espeakup a multi-threaded program. One thread reads from the softsynth
device, queuing text and synthesis commands. The other thread processes
items from the queue.
I have added queueing support so that when we read from the softsynth we
can put the text and commands we have read into a queue. This will
allow us to retry calling espeak_synth() if we fill espeak's internal
buffer.
