Use shared_ptr instead of unique_ptr for elements.

This allow users to pass it into initializer list. Then clang-format
will produce 'acceptable' indentations.

This fixes:
https://github.com/ArthurSonzogni/FTXUI/issues/18

examples/dom/gauge.cpp

@@ -17,14 +17,11 @@ int main(int argc, const char* argv[]) {
   for (float percentage = 0.0f; percentage <= 1.0f; percentage += 0.002f) {
     std::wstring data_downloaded =
         std::to_wstring(int(percentage * 5000)) + L"/5000";
-    // clang-format off
-    auto document =
-        hbox(
-          text(L"downloading:"),
-          gauge(percentage) | flex,
-          text(L" " + data_downloaded)
-        );
-    // clang-format on
+    auto document = hbox({
+        text(L"downloading:"),
+        gauge(percentage) | flex,
+        text(L" " + data_downloaded),
+    });
     auto screen = Screen(100, 1);
     Render(screen, document.get());
     std::cout << reset_position << screen.ToString() << std::flush;