Add Account Role Listings (#198)

I want to list the roles availablew in an account so I can add a member
to the account

tests/Endpoints/AccountRolesTest.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace Endpoints;
+
+use Cloudflare\API\Adapter\Adapter;
+use Cloudflare\API\Endpoints\AccountRoles;
+use TestCase;
+
+class AccountRolesTest extends TestCase
+{
+    public function testListAccountRoles()
+    {
+        $response = $this->getPsr7JsonResponseForFixture('Endpoints/listAccountRoles.json');
+
+        $adapter = $this->getMockBuilder(Adapter::class)->getMock();
+        $adapter->method('get')->willReturn($response);
+
+        $adapter->expects($this->once())
+            ->method('get')
+            ->with($this->equalTo('accounts/023e105f4ecef8ad9ca31a8372d0c353/roles'));
+
+        $roles  = new AccountRoles($adapter);
+        $result = $roles->listAccountRoles('023e105f4ecef8ad9ca31a8372d0c353');
+
+        $this->assertObjectHasAttribute('result', $result);
+        $this->assertObjectHasAttribute('result_info', $result);
+
+        $this->assertEquals('3536bcfad5faccb999b47003c79917fb', $result->result[0]->id);
+        $this->assertEquals(1, $result->result_info->page);
+        $this->assertEquals('3536bcfad5faccb999b47003c79917fb', $roles->getBody()->result[0]->id);
+    }
+}