Add the flag to request a renderer where SDLRenderer::present is synchronized with the refresh rate

Property definitions

sdl2 $ SDLRendererFlags :: presentvsync
	# Add the flag to request a renderer where `SDLRenderer::present` is synchronized with the refresh rate
	fun presentvsync: SDLRendererFlags `{ return self | SDL_RENDERER_PRESENTVSYNC; `}
lib/sdl2/sdl2_base.nit:390,2--391,82