More work on timeouts and racing listeners.

When two listeners are racing to resume the same fiber, the
first should cancel out the other.

examples/tcpserver.janet

@@ -5,10 +5,17 @@
   (def b @"")
   (print "Connection " id "!")
   (while (:read stream 1024 b)
+    (repeat 10 (print "work for " id " ...") (ev/sleep 1))
     (:write stream b)
     (buffer/clear b))
   (printf "Done %v!" id))
 
+(defn spawn-kid
+  "Run handler in a new fiber"
+  [conn]
+  (def f (fiber/new handler))
+  (ev/go f conn))
+
 (print "Starting echo server on 127.0.0.1:8000")
 
 (def server (net/server "127.0.0.1" "8000"))
@@ -16,4 +23,5 @@
 # Run server.
 (while true
   (with [conn (:accept server)]
-    (handler conn)))
+    (spawn-kid conn)
+    (ev/sleep 0.1)))