Add mechanism to register (noisy) signal handler

This allows programs that are waiting on a signal to proceed to
work. Sometimes, there are programs that are waiting for an alarm,
or similar prior to performing I/O.

This was impossible, because signal handlers were never registered
as noisy actors in asio. This allows for an optional named parameter
to be passed with that context.

Author: sargun

packages/signals/signal_handler.pony

@@ -10,19 +10,21 @@ use @pony_asio_event_destroy[None](event: AsioEventID)
 actor SignalHandler
   """
   Listen for a specific signal.
+  If the wait parameter is true, the program will not terminate until the SignalHandler's dispose method is called.
+
   """
   let _notify: SignalNotify
   let _sig: U32
   var _event: AsioEventID
 
-  new create(notify: SignalNotify iso, sig: U32) =>
+  new create(notify: SignalNotify iso, sig: U32, wait: Bool = false) =>
     """
     Create a signal handler.
     """
     _notify = consume notify
     _sig = sig
     _event =
-      @pony_asio_event_create(this, 0, AsioEvent.signal(), sig.u64(), false)
+      @pony_asio_event_create(this, 0, AsioEvent.signal(), sig.u64(), wait)
 
   be raise() =>
     """