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/component/component.hpp

@@ -10,7 +10,7 @@
 #include "ftxui/component/component_base.hpp"  // for Component, Components
 #include "ftxui/component/component_options.hpp"  // for ButtonOption, CheckboxOption, MenuOption
 #include "ftxui/dom/elements.hpp"  // for Element
-#include "ftxui/util/ref.hpp"  // for Ref, ConstStringRef, ConstStringListRef, StringRef
+#include "ftxui/util/ref.hpp"  // for ConstRef, Ref, ConstStringRef, ConstStringListRef, StringRef
 
 namespace ftxui {
 struct ButtonOption;
@@ -82,6 +82,9 @@ Component Slider(ConstStringRef label,
                  ConstRef<long> min = 0l,
                  ConstRef<long> max = 100l,
                  ConstRef<long> increment = 5l);
+// General slider type without support for a `label`.
+template <typename T>  // T = {int, float, long}
+Component Slider(SliderOption<T> options = {});
 
 Component ResizableSplitLeft(Component main, Component back, int* main_size);
 Component ResizableSplitRight(Component main, Component back, int* main_size);

include/ftxui/component/component_options.hpp

@@ -3,11 +3,11 @@
 
 #include <chrono>                         // for milliseconds
 #include <ftxui/component/animation.hpp>  // for Duration, QuadraticInOut, Function
-#include <ftxui/dom/elements.hpp>         // for Element
-#include <ftxui/util/ref.hpp>             // for Ref
-#include <functional>                     // for function
-#include <optional>                       // for optional
-#include <string>                         // for string
+#include <ftxui/dom/elements.hpp>  // for Element, GaugeDirection, GaugeDirection::Right
+#include <ftxui/util/ref.hpp>  // for Ref, ConstRef
+#include <functional>          // for function
+#include <optional>            // for optional
+#include <string>              // for string
 
 #include "ftxui/screen/color.hpp"  // for Color, Color::GrayDark, Color::White
 
@@ -164,6 +164,19 @@ struct RadioboxOption {
   Ref<int> focused_entry = 0;
 };
 
+// @brief Option for the `Slider` component.
+// @ingroup component
+template <typename T>
+struct SliderOption {
+  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;
+};
+
 }  // namespace ftxui
 
 #endif /* end of include guard: FTXUI_COMPONENT_COMPONENT_OPTIONS_HPP */

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