Add Blink. Refactor examples.

examples/dom/vbox_hbox.cpp

@@ -0,0 +1,36 @@
+#include "ftxui/screen.hpp"
+#include "ftxui/dom/elements.hpp"
+#include <iostream>
+
+int main(int argc, const char *argv[])
+{
+  using namespace ftxui::dom;
+  auto document =
+    vbox(
+      hbox(
+        text(L"north-west"),
+        flex(),
+        text(L"north-east")
+      ),
+      flex(),
+      hbox(
+        hbox(
+          flex(),
+          text(L"center"),
+          flex()
+        )
+      ),
+      flex(),
+      hbox(
+        text(L"south-west"),
+        flex(),
+        text(L"south-east")
+      )
+    );
+  auto screen = ftxui::Screen::TerminalFullscreen();
+  Render(screen, document.get());
+
+  std::cout << screen.ToString();
+
+  return 0;
+}