[racket] sound + universe report: success.

Q: is it possible to test the length of 'momentary' sounds programmatically? 

Proposed design: 

 big-bang accepts another clause: 

    [sounds pop meow bark]
	-- constraint: pop.wav, meow.wav, bark.wav exist in the current directory 
	-- constraint: they are momentary sounds 

 all handlers are allowed to return a 

    (with-sound world-state soundname)

 response. Meaning: if the 'sounds' clause is available and if the soundname is mentioned in that clause, play the sound (just like we render the world state). 

Comments? -- Matthias