Go-like channels for atomically passing information between threads.

(make-channel) ; make new channel
(make-channel 2) ; make new channel with max size of 2 (untested)

(-> chan item) ; send item to channel
(<- chan) ; receive from channel (values item is-not-closed)
(release chan) ; close channel
(closed chan) ; is channel closed


(make-dispatcher) ; make dispatcher
(hook disp name lambda) ; add hook
(sig name (optional value)) ; signal name in parallel
(sig-serial name (optional value)) ; signal name in serial