Unit tests and I/O bindings (#8)

* Added composer config, added IO/error tests using phpunit

* Added ApiGen doc comments

* Added test to ensure last_error is not set from loading up the CRT

lib/io.php

@@ -0,0 +1,27 @@
+<?php
+
+require_once('crt.php');
+
+final class EventLoopGroupOptions {
+    /**
+     * @var int $num_threads - Number of worker threads in the EventLoopGroup. Defaults to 0/1 per logical core.
+     */
+    public $num_threads = 0;
+}
+
+/**
+ * Represents 1 or more event loops (1 per thread) for doing I/O and background tasks.
+ * Typically, every application has one EventLoopGroup.
+ */
+final class EventLoopGroup extends NativeResource {
+    function __construct($options) {
+        parent::__construct();
+        $this->acquire(self::$crt->event_loop_group_new($options->num_threads));
+    }
+
+    function __destruct() {
+        self::$crt->event_loop_group_release($this->native);
+        $this->release();
+        parent::__destruct();
+    }
+}