add cursor-offset (pagination)

- simply added parameter to existing implementation

Author: johguentner

src/Endpoints/Endpoint.php

@@ -169,8 +169,8 @@ public function limit(int $limit): Endpoint
      */
     public function offset(StartCursor $startCursor): Endpoint
     {
-        // toDo
-        throw HandlingException::instance('Not implemented yet.', compact($startCursor));
+        $this->startCursor = $startCursor;
+        return $this;
     }
 
 }

src/Query/StartCursor.php

@@ -21,4 +21,8 @@ public function __construct(string $cursor)
     {
         $this->cursor = $cursor;
     }
+
+    public function __toString() {
+        return $this->cursor;
+    }
 }