Add a real toString

Author: aheritier

src/main/java/org/zendesk/client/v2/model/events/AgentMacroReferenceEvent.java

@@ -40,7 +40,11 @@ public void setVia(Via via) {
 
     @Override
     public String toString() {
-        // TODO A real implementation
-        return null;
+        final StringBuilder sb = new StringBuilder("AgentMacroReferenceEvent{");
+        sb.append("macroId=").append(macroId);
+        sb.append(", macroTitle='").append(macroTitle).append('\'');
+        sb.append(", via=").append(via);
+        sb.append('}');
+        return sb.toString();
     }
 }