* Added my custom version of Approvals gem for use in developing this
gem.
** Added some initial bmp of approvals.
* Added SDL2::Struct::cast(something)
* Updated SDL2::Color member readers/writers
* Added SDL2::PixelFormat#map
* Handled nil alpha case for SDL2::PixelFormat#map_rgba
* Added member reader/writers and ::cast to SDL2::Point
* Fixed POWERSTATE enum declaration.
* Added SDL2::Rect::cast
* Documented SDL2::SCANCODE
* SDL2::Surface:
** Added type-sanatizing to #blit_in, #blit_out, #[set|get]_color_key
** Generalized interface for #set_color_key
** Generalized interface for #get_color_key
** Added #fill_rect
** Fixed mistake in SDL2::save_bmp
** Added boolean version of SDL2::get_color_key
* Updated test examples.