Add garbage collection example with iterators

examples/iterators/emitter-gc.php

@@ -0,0 +1,34 @@
+#!/usr/bin/env php
+<?php
+
+require __DIR__ . '/../../vendor/autoload.php';
+
+use Amp\Delayed;
+use Amp\Emitter;
+use Amp\Loop;
+
+Loop::run(function () {
+    $emitter = new Emitter;
+
+    Loop::defer(function () use ($emitter) {
+        try {
+            yield $emitter->emit(1);
+            print "Emit done.\n";
+            yield $emitter->emit(2);
+            print "Never reached...\n";
+            $emitter->complete();
+        } finally {
+            print "Garbage collected...\n";
+        }
+    });
+
+    $iterator = $emitter->iterate();
+    yield $iterator->advance();
+    yield $iterator->advance();
+    yield new Amp\Delayed(0);
+
+    unset($emitter, $iterator);
+    gc_collect_cycles();
+
+    print "Done.\n";
+});