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/psr/container/src/ContainerInterface.php

@@ -0,0 +1,37 @@
+<?php
+/**
+ * @license http://www.opensource.org/licenses/mit-license.php MIT (see the LICENSE file)
+ */
+
+namespace Psr\Container;
+
+/**
+ * Describes the interface of a container that exposes methods to read its entries.
+ */
+interface ContainerInterface
+{
+    /**
+     * Finds an entry of the container by its identifier and returns it.
+     *
+     * @param string $id Identifier of the entry to look for.
+     *
+     * @throws NotFoundExceptionInterface  No entry was found for **this** identifier.
+     * @throws ContainerExceptionInterface Error while retrieving the entry.
+     *
+     * @return mixed Entry.
+     */
+    public function get($id);
+
+    /**
+     * Returns true if the container can return an entry for the given identifier.
+     * Returns false otherwise.
+     *
+     * `has($id)` returning true does not mean that `get($id)` will not throw an exception.
+     * It does however mean that `get($id)` will not throw a `NotFoundExceptionInterface`.
+     *
+     * @param string $id Identifier of the entry to look for.
+     *
+     * @return bool
+     */
+    public function has($id);
+}