Fixed timer implementation

examples/timers.php

@@ -30,9 +30,15 @@ class MyShell extends Shell
         $this->pushContext($context);
         $this->updatePrompt();
 
-        $this->addTimer(5000, function () {
+        $t1 = $this->addTimer(5000, function () {
             echo "5 seconds\n";
         });
+        $app = $this;
+        $t2 = $this->addTimer(15000, function () use ($t1, $app) {
+            echo "Removing timers...\n";
+            $app->removeTimer($t1);
+        });
+        
     }
     
     protected function updatePrompt()