feat(er): allow multiple constraints on attributes

little changes in grammar to get a list of constraints (PK, FK or UK), so little changes in renderer to handle this list

demos/er.html

@@ -71,6 +71,20 @@
     </pre>
     <hr />
 
+    <pre class="mermaid">
+      erDiagram
+        "HOSPITAL" {
+          int id PK
+          int doctor_id PK,FK
+          string address UK
+          string name
+          string phone_number
+          string fax_number
+        }
+      </pre
+    >
+    <hr />
+
     <script src="./mermaid.js"></script>
     <script type="module">
       mermaid.initialize({