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.

examples/CMakeLists.txt

@@ -4,6 +4,9 @@ function(example name)
   target_link_libraries(ftxui_example_${name} PUBLIC ${DIRECTORY_LIB})
   file(RELATIVE_PATH dir ${EXAMPLES_DIR} ${CMAKE_CURRENT_SOURCE_DIR})
   set_property(GLOBAL APPEND PROPERTY FTXUI::EXAMPLES ${dir}/${name})
+  set_target_properties(ftxui_example_${name} PROPERTIES
+    CXX_STANDARD 20
+  )
 endfunction(example)
 
 add_subdirectory(component)