window-keyboard-grab?
window-keyboard-grab-set!
window-mouse-grab?
window-mouse-grab-set!

- Removed define-versioned-enum-mappings.
- define-enum-mappings supports feature identifiers like
  define-versioned-enum-mappings did.
- Versioned enum mappings no longer require hash tables, so
  performance is improved.

They now accept an optoinal delay procedure, defaulting to sdl2:delay!.
Users can provide a different delay procedure in case they are using
SRFI-18 multithreading.

get-yuv-conversion-mode
get-yuv-conversion-mode-raw
yuv-conversion-mode-set!

video-init!
video-quit!
get-num-video-drivers
get-video-driver
get-current-video-driver

get-num-display-modes
get-display-mode
get-current-display-mode
get-closest-display-mode
get-desktop-display-mode

With SDL 2.0.9+ it wraps SDL_HasColorKey. With older versions of SDL
it calls SDL_GetColorKey and checks the return status code.

With SDL 2.0.6+ it wraps SDL_DuplicateSurface. With older versions
of SDL it calls SDL_ConvertSurface with the same format, which is
how SDL_DuplicateSurface is implemented anyway.