Add documentations to every public functions.

src/ftxui/dom/text.cpp

@@ -17,6 +17,7 @@
 
 namespace ftxui {
 
+namespace {
 using ftxui::Screen;
 
 class Text : public Node {
@@ -80,6 +81,8 @@ class VText : public Node {
   int width_ = 1;
 };
 
+}  // namespace
+
 /// @brief Display a piece of UTF8 encoded unicode text.
 /// @ingroup dom
 /// @see ftxui::to_wstring