added transaction fee support to sale class

tests/PayPal/Test/Api/TransactionFeeTest.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace PayPal\Test\Api;
+
+use PayPal\Api\TransactionFee;
+
+class TransactionFeeTest extends \PHPUnit_Framework_TestCase
+{
+    public function testGetterSetter()
+    {
+        $tfee = new TransactionFee();
+        $tfee->setCurrency('AUD');
+        $this->assertEquals('AUD', $tfee->getCurrency());
+
+        $tfee->setValue('0.10');
+        $this->assertEquals('0.10', $tfee->getValue());
+    }
+}