Add pear modules, mail and net_smtp via composer (#93)

Add pear modules, mail and net_smtp via composer, remove php 5.6 build due to phpunit 6

lib/composer/vendor/symfony/debug/Tests/Fixtures/InternalInterface.php

@@ -0,0 +1,10 @@
+<?php
+
+namespace Symfony\Component\Debug\Tests\Fixtures;
+
+/**
+ * @internal
+ */
+interface InternalInterface
+{
+}