add subscription process endpoint

src/Entities/Subscription.php

@@ -0,0 +1,13 @@
+<?php
+
+namespace D3\KlicktippPhpClient\Entities;
+
+use Doctrine\Common\Collections\ArrayCollection;
+
+class Subscription extends ArrayCollection
+{
+    public function getId(): string
+    {
+        return $this->get('id');
+    }
+}

src/Klicktipp.php

@@ -18,6 +18,7 @@ namespace D3\KlicktippPhpClient;
 use D3\KlicktippPhpClient\Exceptions\BaseException;
 use D3\KlicktippPhpClient\Resources\Account;
 use D3\KlicktippPhpClient\Resources\Subscriber;
+use D3\KlicktippPhpClient\Resources\SubscriptionProcess;
 use D3\KlicktippPhpClient\Resources\Tag;
 use GuzzleHttp\ClientInterface;
 use GuzzleHttp\Exception\GuzzleException;
@@ -57,6 +58,11 @@ class Klicktipp
         return $this->connection;
     }
 
+    public function subscription(): SubscriptionProcess
+    {
+        return new SubscriptionProcess($this->getConnection());
+    }
+
     public function account(): Account
     {
         return new Account($this->getConnection());

src/Resources/SubscriptionProcess.php

@@ -0,0 +1,54 @@
+<?php
+
+namespace D3\KlicktippPhpClient\Resources;
+
+use D3\KlicktippPhpClient\Entities\Subscription as SubscriptionEntity;
+use D3\KlicktippPhpClient\Exceptions\BaseException;
+use GuzzleHttp\Exception\GuzzleException;
+use GuzzleHttp\RequestOptions;
+
+class SubscriptionProcess extends Model
+{
+    /**
+     * @throws BaseException|GuzzleException
+     */
+    public function index(): array
+    {
+        return $this->connection->requestAndParse(
+            'GET',
+            'list'
+        );
+    }
+
+    /**
+     * @throws BaseException|GuzzleException
+     */
+    public function get(string $listId): SubscriptionEntity
+    {
+        $data = $this->connection->requestAndParse(
+            'GET',
+            'list/'.urlencode(trim($listId))
+        );
+
+        return new SubscriptionEntity($data);
+    }
+
+    /**
+     * @throws BaseException|GuzzleException
+     */
+    public function redirect(string $listId, string $email): string
+    {
+        return current(
+            $this->connection->requestAndParse(
+                'POST',
+                'list/redirect',
+                [
+                    RequestOptions::FORM_PARAMS => [
+                        'listid'    => trim($listId),
+                        'email'     => trim($email),
+                    ]
+                ]
+            )
+        );
+    }
+}