implemented create event + create offset

src/diagram.typ

@@ -123,6 +123,16 @@
         elmt: elmt,
         i: i
       )
+    } else if elmt.type == "evt" {
+      let par = elmt.participant
+      if not participant._exists(participants, par) {
+        let p = _par(par, from-start: elmt.event != "create").first()
+        participants.push(p)
+      
+      } else if elmt.event == "create" {
+        let i = participants.position(p => p.name == par)
+        participants.at(i).from-start = false
+      }
     }
   }
   linked = linked.dedup()