jambonz => websocket server

An tts:streaming-event message is sent by jambonz to indicate a streaming event

The message shall contain an event_type field with one of the following values:

• stream_open: tokens are now being streamed to the synthesizer; any tokens received before this event would have been queued and are now being sent
• stream_closed: tokens are no longer being streamed to the synthesizer, but the application may continue sending them; when the stream is next opened the queued tokens will be sent.
• stream_paused: the token buffer is full and the application should discontinue sending tokens
• stream_resumed: the application may resume sending tokens