feat(page): add pagecreated event to allow listening for new pages

src/events.ts

@@ -41,6 +41,7 @@ export const Events = {
     FrameDetached: 'framedetached',
     FrameNavigated: 'framenavigated',
     Load: 'load',
+    PageCreated: 'pagecreated',
     Popup: 'popup',
     WebSocket: 'websocket',
     WorkerCreated: 'workercreated',

src/page.ts

@@ -139,6 +139,7 @@ export class Page extends platform.EventEmitter {
     if (delegate.pdf)
       this.pdf = delegate.pdf.bind(delegate);
     this.coverage = delegate.coverage();
+    this.emit(Events.Page.PageCreated);
   }
 
   _didClose() {