Add support for nxxm.

[nxxm](https://nxxm.github.io)

tests/text_test.cpp

@@ -0,0 +1,46 @@
+#include "ftxui/dom/elements.hpp"
+#include "ftxui/screen/screen.hpp"
+#include "gtest/gtest.h"
+
+using namespace ftxui;
+using namespace ftxui;
+
+TEST(TextTest, ScreenHeightSmaller) {
+  auto element = text(L"test");
+  Screen screen(2, 0);
+  Render(screen, element.get());
+
+  EXPECT_EQ("", screen.ToString());
+}
+
+TEST(TextTest, ScreenSmaller) {
+  auto element = text(L"test");
+  Screen screen(2, 1);
+  Render(screen, element.get());
+
+  EXPECT_EQ("te", screen.ToString());
+}
+
+TEST(TextTest, ScreenFit) {
+  auto element = text(L"test");
+  Screen screen(4, 1);
+  Render(screen, element.get());
+
+  EXPECT_EQ("test", screen.ToString());
+}
+
+TEST(TextTest, ScreenBigger) {
+  auto element = text(L"test");
+  Screen screen(6, 1);
+  Render(screen, element.get());
+
+  EXPECT_EQ("test  ", screen.ToString());
+}
+
+TEST(TextTest, ScreenBigger2) {
+  auto element = text(L"test");
+  Screen screen(6, 2);
+  Render(screen, element.get());
+
+  EXPECT_EQ("test  \n      ", screen.ToString());
+}