code: added ga tracker to web html demo

web/eco2d.html

@@ -27,6 +27,16 @@
     <meta name="twitter:url" content="https://github.com/zpl-c/eco2d">
     <meta name="twitter:description" content="Small C99 2D game engine with a focus on prototyping">
 
+    <!-- Google tag (gtag.js) -->
+    <script async src="https://www.googletagmanager.com/gtag/js?id=G-R1QS3P3D1T"></script>
+    <script>
+      window.dataLayer = window.dataLayer || [];
+      function gtag(){dataLayer.push(arguments);}
+      gtag('js', new Date());
+
+      gtag('config', 'G-R1QS3P3D1T');
+    </script>
+
     <style>
         html, body { margin: 0px; padding: 0px; background-color: black; width: 100%; height: 100%;}
         canvas.emscripten {