feat(docs) improvements to examples

* examples are now loaded only when they are visible on your screen
* stylistic improvements
* support for a description

docs/_templates/page.html

@@ -51,5 +51,32 @@ document.addEventListener('DOMContentLoaded', (event) => {
     });
     
 })
+document.addEventListener('DOMContentLoaded', (event) => {
+    function onIntersection(entries) {
+        entries.forEach(entry => {
+            let currentlyLoaded = entry.target.getAttribute("data-is-loaded") == "true";
+            let shouldBeLoaded = entry.intersectionRatio > 0;
+            if(currentlyLoaded != shouldBeLoaded) {
+                entry.target.setAttribute("data-is-loaded", shouldBeLoaded);
+                if(shouldBeLoaded) {
+                    let iframe = document.createElement("iframe");
+                    iframe.src = entry.target.getAttribute("data-real-src");
+                    entry.target.appendChild(iframe);
+                } else {
+                    let iframe = entry.target.querySelector("iframe");
+                    iframe.parentNode.removeChild(iframe);
+                }
+            }
+        });
+    }
+    const config = {
+        rootMargin: '50px 0px',
+        threshold: 0.01
+    };
+    let observer = new IntersectionObserver(onIntersection, config);
+    document.querySelectorAll(".lv-example").forEach(iframe => {
+        observer.observe(iframe);
+    });
+});
 </script>
 {% endblock %}