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/tests/tests.inc

@@ -0,0 +1,9 @@
+<?php
+
+// Ensure any version of PHPUnit works, since phpunit5 is the last one that
+// works with PHP5.6
+if (!class_exists('PHPUnit_Framework_TestCase') &&
+  class_exists('\\PHPUnit\\Framework\\TestCase')) {
+    abstract class PHPUnit_Framework_TestCase extends \PHPUnit\Framework\TestCase {
+    }
+}