Handle SDL surface formats

[JD557]

Right now, SdlSurface expects all Surfaces to be SDL_PIXELFORMAT_RGBA32, which is a problem when interacting with other libraries, such as SDL image.

For example, to load an image, one needs to do:

  def loadImage(path: CString): RamSurface =
    val originalSurface = IMG_Load(path)
    if (originalSurface == null) throw new RuntimeException("Failed to load image")
    val formattedSurface = SDL_ConvertSurfaceFormat(originalSurface, SDL_PixelFormatEnum.SDL_PIXELFORMAT_RGBA32.uint, 0.toUInt)
    val ramSurface = SdlSurface.withRawData(formattedSurface)(_.toRamSurface())
    SDL_FreeSurface(originalSurface)
    SDL_FreeSurface(formattedSurface)
    ramSurface

There should at least be some helper to convert a Ptr[SDL_Surface] to a RamSurface and take care of converting the surface if needed and free any temporary objects.

A smart constructor (or multiple SdlSurface implementations that support different formats) could also be nice, as views over surfaces can also be broken.