Feature: hscroll_indicator (#753)

This is the symetrical of `vscroll_indicator`.

Requested by @ibrahimnasson.

Fixed:https://github.com/ArthurSonzogni/FTXUI/issues/752

src/ftxui/dom/gauge.cpp

@@ -159,7 +159,7 @@ class Gauge : public Node {
   Direction direction_;
 };
 
-}  // namespace ftxui
+}  // namespace
 
 /// @brief Draw a high definition progress bar progressing in specified
 /// direction.