Mark toString() method as deprecated, scheduled for removal in 4.0.0

src/Uuid.php

@@ -590,6 +590,14 @@ class Uuid implements UuidInterface
         return null;
     }
 
+    /**
+     * {@inheritdoc}
+     *
+     * @deprecated In ramsey/uuid 4.0.0, this method will be replaced with the
+     *     __toString() magic method, which is already available on this class.
+     *     The new recommendation is to cast Uuid objects to string, rather than
+     *     calling `toString()`.
+     */
     public function toString()
     {
         return $this->codec->encode($this);