Add UTF8 support and a better xterm parsing.

This fixes: https://github.com/ArthurSonzogni/FTXUI/issues/2

include/ftxui/dom/elements.hpp

@@ -36,7 +36,7 @@ Decorator bgcolor(Color);
 Element color(Color, Element);
 Element bgcolor(Color, Element);
 
-// --- Layout ---
+// --- Layout is
 // Horizontal, Vertical or stacked set of elements.
 Element hbox(Elements);
 Element vbox(Elements);