feat: Provide code fragments feature (#748)

docs/_media/example.js

@@ -0,0 +1,16 @@
+import fetch from 'fetch'
+
+const URL = 'https://example.com'
+const PORT = 8080
+
+/// [demo]
+const result = fetch(`${URL}:${PORT}`)
+  .then(function(response) {
+    return response.json();
+  })
+  .then(function(myJson) {
+    console.log(JSON.stringify(myJson));
+  });
+/// [demo]
+
+result.then(console.log).catch(console.error)