[ab] Update to sdl:with-events

[Luke Crook]

I've made a change to the syntax of sdl:with-events. It now takes keyword 
parameters instead of a fixed arg list for each event.

For example:

      (sdl:with-events ()
	(:quit () t)
	(:keydown (:key key-press)
		  (if (sdl:key= key-press :SDLK_ESCAPE)
		      (sdl:push-quitevent)))
	(:videoexpose () (sdl:update-display))))))

instead of the old:

      (sdl:with-events ()
	(:quit () t)
	(:keydown (state scancode key-press mod unicode)
		  (if (sdl:key= key-press :SDLK_ESCAPE)
		      (sdl:push-quitevent)))
	(:videoexpose () (sdl:update-display))))))

Use (documentation 'sdl:with-events 'function) to see the keywords for each 
event type.

- Luke