Updated Invoicing APIs

- Updated Model objects.
- Updated Samples.
- Updated Tests.

lib/PayPal/Api/FileAttachment.php

@@ -0,0 +1,67 @@
+<?php
+
+namespace PayPal\Api;
+
+use PayPal\Common\PayPalModel;
+use PayPal\Validation\UrlValidator;
+
+/**
+ * Class FileAttachment
+ *
+ * File attached to an invoice or template
+ *
+ * @package PayPal\Api
+ *
+ * @property string name
+ * @property string url
+ */
+class FileAttachment extends PayPalModel
+{
+    /**
+     * Name of the file attached.
+     *
+     * @param string $name
+     * 
+     * @return $this
+     */
+    public function setName($name)
+    {
+        $this->name = $name;
+        return $this;
+    }
+
+    /**
+     * Name of the file attached.
+     *
+     * @return string
+     */
+    public function getName()
+    {
+        return $this->name;
+    }
+
+    /**
+     * URL of the attached file that can be downloaded.
+     *
+     * @param string $url
+     * @throws \InvalidArgumentException
+     * @return $this
+     */
+    public function setUrl($url)
+    {
+        UrlValidator::validate($url, "Url");
+        $this->url = $url;
+        return $this;
+    }
+
+    /**
+     * URL of the attached file that can be downloaded.
+     *
+     * @return string
+     */
+    public function getUrl()
+    {
+        return $this->url;
+    }
+
+}