Feature: Slider in any directions. (#468)

Add the `SliderOption` option supporting:
```cpp
{
  Ref<T> value;
  ConstRef<T> min = T(0);
  ConstRef<T> max = T(100);
  ConstRef<T> increment = (max() - min()) / 20;
  GaugeDirection direction = GaugeDirection::Right;
  Color color_active = Color::White;
  Color color_inactive = Color::GrayDark;
};
```

In particular, this supports multiple direction. This resolves:
https://github.com/ArthurSonzogni/FTXUI/issues/467

This one do not support adding a label. The old constructors can still
be used to have a label.

include/ftxui/screen/screen.hpp

@@ -2,7 +2,7 @@
 #define FTXUI_SCREEN_SCREEN_HPP
 
 #include <memory>
-#include <string>  // for string, allocator, basic_string
+#include <string>  // for allocator, string, basic_string
 #include <vector>  // for vector
 
 #include "ftxui/screen/box.hpp"       // for Box