Add UTF8 support and a better xterm parsing.

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

src/ftxui/screen/terminal.cpp

@@ -1,7 +1,7 @@
-#include <iostream>
-#include <sys/ioctl.h>
 #include <stdio.h>
+#include <sys/ioctl.h>
 #include <unistd.h>
+#include <iostream>
 
 #include "ftxui/screen/terminal.hpp"
 
@@ -9,7 +9,7 @@ namespace ftxui {
 
 Terminal::Dimensions Terminal::Size() {
 #ifdef __EMSCRIPTEN__
-  return Dimensions{80,43};
+  return Dimensions{80, 43};
 #else
   winsize w;
   ioctl(STDOUT_FILENO, TIOCGWINSZ, &w);
@@ -17,4 +17,4 @@ Terminal::Dimensions Terminal::Size() {
 #endif
 }
 
-} // namespace ftxui
+}  // namespace ftxui