1.15.0

• Dropped support for Python 2, Python 3.9 or above is now required.
• Added support for ColouredText titles in MultiColumnLIstBox.
• Added gutter option to Layout.
• Added speed option to Sprite.
• Fixed bug where moving focus between Frames resulted in no current focus.
• Fixed internal state of RadioButton values to be consistent with selection.
• Fixed handling of zero width modifiers.
• Fixed image conversion to use modern PIL API and sort off-by-one height error.
• Fixed parser bug returning list instead of colour tuple.