Enabled Billing Plans and Agreements APIs

- Added API Classes, Samples, and Tests
- Updated Functional Tests
- Updated Documentation with new SDK Name
- Updated Few Samples to use newer nicer result page

sample/billing/GetPlan.php

@@ -0,0 +1,25 @@
+<?php
+
+// # Get Plan Sample
+//
+// This sample code demonstrate how you can get a billing plan, as documented here at:
+// https://developer.paypal.com/webapps/developer/docs/api/#retrieve-a-plan
+// API used: /v1/payments/billing-plans
+
+// Retrieving the Plan object from Create Plan Sample
+/** @var Plan $createdPlan */
+$createdPlan = require 'CreatePlan.php';
+
+use PayPal\Api\Plan;
+
+try {
+    $plan = Plan::get($createdPlan->getId(), $apiContext);
+} catch (PayPal\Exception\PPConnectionException $ex) {
+    echo "Exception: " . $ex->getMessage() . PHP_EOL;
+    var_dump($ex->getData());
+    exit(1);
+}
+
+ResultPrinter::printResult("Retrieved a Plan", "Plan", $plan->getId(), null, $plan);
+
+return $plan;