Add Surface rotozoom Support

// rotozoom.go
package sdl

// #cgo pkg-config: sdl SDL_gfx
// #include <SDL.h>
// #include <SDL_rotozoom.h>
import "C"

func (s *Surface) RotoZoom(angle, zoom float64, smooth int32) *Surface {
    s.mutex.Lock()
    defer s.mutex.Unlock()
    return wrap(C.rotozoomSurface(s.cSurface, C.double(angle), C.double(zoom), C.int(smooth)))
}