closes #19: kill underlings with system level interrupts

tests/kill.ce

@@ -0,0 +1,15 @@
+// This tests forceful killing of an underling that may even be in the middle of a turn
+
+$_.start(e => {
+  log.console(`got message from hanger: ${e.type}`)
+  if (e.type == 'greet')
+    $_.delay(_ => {
+      log.console(`sending stop message to hanger`)
+      $_.stop(e.actor)
+    }, 1)
+    
+  if (e.type == 'disrupt') {
+    log.console(`underling successfully killed.`)
+    $_.stop()
+  }
+}, 'hang')