[#2] Create basic EnvelopeInterface

src/Envelope.php

@@ -15,7 +15,7 @@
 use Doctrine\Common\Collections\ArrayCollection;
 use Doctrine\Common\Collections\Collection;
 
-class Envelope
+class Envelope implements EnvelopeInterface
 {
     /**
      * @var \Doctrine\Common\Collections\Collection

src/EnvelopeInterface.php

@@ -0,0 +1,25 @@
+<?php
+
+/*
+ * This file is part of the DigiDoc package.
+ *
+ * (c) Kristen Gilden <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace KG\DigiDoc;
+
+interface EnvelopeInterface
+{
+    /**
+     * @return \Iterator
+     */
+    public function getFiles();
+
+    /**
+     * @return \Iterator
+     */
+    public function getSignatures();
+}