Add ability to hide mouse cursor
Created by: alexander-b
For games that use mouse input, it's pretty much necessary to be able to use a custom cursor. I suggest adding sol.input.show_cursor(), sol.input.hide_cursor(), and sol.input.is_cursor_visible(). These would correspond to int SDL_ShowCursor(1), SDL_ShowCursor(0), and SDL_ShowCursor(-1) respectively. See https://wiki.libsdl.org/SDL_ShowCursor.