start

Starts (or restarts) the timer. If the timer is already running, its alarm time is not changed.

• (send a-timer start m just-once?) -> void
      m : exact integer in [0, 1000000000]
      just-once? = #f : boolean

  The timer's alarm expires after m milliseconds, at which point notify is called (on an event boundary). If just-once? is #f, the timer expires every m milliseconds until the timer is explictly stopped; otherwise, the timer expires only once.