feat: add name field to the actors

demos/sequence.html

@@ -187,6 +187,13 @@
         Note left of Bob: Alice/Bob Note
       end
     </pre>
+    <pre class="mermaid">
+      sequenceDiagram
+        actor Alice
+        actor John
+        Alice-xJohn: Hello John, how are you?
+        John--xAlice: Great!
+    </pre>
 
     <script type="module">
       import mermaid from './mermaid.esm.mjs';