Pygame-menu

- Fix widget being selected if not selectable.
- Added collide method on the scroll widget.
- Added variable scroll speed if SHIFT is pressed.

- Fix deprecation warning, 213.

- Fix deprecation warning, 211.

- Added image background example.
- Added `set_background_color_opacity` method to Theme class.
- Added `None` to area parameter of `draw` BaseImage method class.

- Added widgets `.set_attribute()` and `.get_attribute()` methods.
- Move Menu `back_box` constructor to `menubar_close_button` Theme, 204.
- Improve pygame error messages.
- Improve title string casting.
- Added Button `.update_callback()` method.
- Fix pygame min version, 206.

- Ignore mouse if selection time is lower than the repeat limit.
- Added selection time to widgets, use `widget.get_selected_time()`.
- Added font antialias to themes.
- Added `widget.set_title()` method.
- Improve compatibility with pygame v2.
- Improve text input history on cut/copy.
- Improve auto separator completion in ColorInput.
- Improve method general assertions.
- Fixed issues 198, 199, 202, 203.